Quick answers:

Is the the end of SEO?
No

I wonder how SE do that - How do they learn our search behavior and if it says something.
All kinds of tracking - browsers, toolbars, cookies, Google accounts, etc, etc.

I know that search history is stored somewhere but for a single PC sometimes could be more than one user.
Yes, it can be. It matters more to the individual than to the large aggregate data that Google looks at

Is it legal?
So far

Is it social?
More and more

What are the consequences?
We're learning that right now.

Each of these "quick questions" has already generated hundreds - maybe thousands - of threads on WebmasterWorld. The Site Search [webmasterworld.com] will uncover a lot of discussion and I'm not sure there's a lot new to say right now.

The important news here is that Google will soon be expanding personalization in new ways. Matt indicated that the SSL keyword referrer issue will easier to understand once we see what is waiting in the wings.

So we(not everyone minds, i'm speaking for those that do) need a fresh guide on how to preserve generic results. In short - a guide on how to block Google from monitoring you to tailor your results.

- Step #1, shut down all of your Google products since they all gather information?

Matt Cutts, Goolge, hints that Search is becoming more personal and will grow more personal in the coming months.

Gee. I don't think anyone around here would ever have suspected that.

There are at least two different issues here, as I see it. One is how to stop seeing personalized results. Here's Google's Help page on the topic: Turning off search history personalization [google.com]

A second issue is to stop Google collecting the data in the first place. Remembering that Google also owns Doubleclick and Youtube among other properties, this gets pretty complicated pretty fast. Here's one place to begin research: Google Privacy Center [google.com]

Think part of what Zivush is getting as it that in the future it could be difficult in a traditional SEO sense to optimize for search terms like say 'red widgets'. Do you appear #1 or #2? Well with a high degree of personalization (and not just the historical stuff we're seeing now) this could be wildly inconsistent. Maybe google puts you into a 'old person' profile based on your search history and determines old people would be better served by widgetx.com for 'red widgets', while young people would be better served by widgety.com.

Ton of potential with personalization which we're seeing a little with search history and localization, but yeah it will make doing SEO a mess if implemented to a significant factor, because you won't know where you really place in the SERP's and therefore won't know how (at least not easily) to improve such rankings.

I came across this earlier and thought this was a worthwhile read - an interview with a G employee:

[stonetemple.com...]

Personalization has to be looked at in conjunction with Google's expressed policy of also predicting your intentions ("we'll know what you want before you know what you want").

With that in the immediate future, the idea of "traditional SEO" will be an oxymoron, as what worked yesterday will not work tomorrow. So SEO itself will have to be re-defined in light of SERPs that display differently for different people. While I'm sure that there will be individuals who will hold the wide range of SEO skills to pull it off, more likely will be SEO teams with each team member having highly specialized expertise: page design, social media, brand building, video integration, link building, customer behavior patterns, etc.

All of which means that for many smaller sites, with less financial resources, the only path forward may be to forget SEO, forget Google, and instead build the site you want to build, the way you want to build it... and hope for the best.

..............................

I made a simple search now and found an interesting (new?) search engine called Blekko, The "Slashtag" Spam free Search Engine.
What I learn is that as a user, YOU can personalize the search results based on your preference.
You actually list websites and search in them based on keywords.
I think this might be a good search experience, only if many users bring their interests etc.

I guess that Google/Bing try to automate this option for you as a user.

see also an article by SELand- [searchengineland.com ]

Thinking out load, might be that big search engines are in cross-road trying to decide whether to make the search experience more social or more personal.
Facebook & Twitter may say: Search must Be more social! (friend-like, based on social signals search)
While others (Still shaking from the social networks power) altering with more 'personal touch' to the search.

What makes it almost impossible for new sites to enter and grow unless making high investment in social networks, branding and site's content quality etc.

Personalized search means a watered down, bland, predictable and boring end result. It says to me that it's an admission that the algo method is unable to do the job and that you get the keys (and your friends) to decide which sites are good enough to show up on your "personalized" Google search results. The onus is on you, me and your circle. The onus isn't on Google. Your results suck? Get new friends or tell them that their taste in art sucks. It's like judging a best food. The more influence other people have on what you see, the more clone like you and I become. Well I say F off friends on mine. I don't give a S what sites you like. I like what I like. I used Google to find good and unique sites.

It's becoming quite clear to me. Public education is needed. I'm sure the general public will eventually understand that what product they used for the past 5+ years is going in an opposite direction. Those search results are becoming less and less of what people wanted. It will take time. Google wasn't built on personalization. They were built on being smart and finding good sites. Not popular sites. Any idiot can do that.

As far as I'm concerned, the more my friend can influence what I see on page one, the more I believe that this is becoming nothing more than a virus.

I find the whole personalized search thing very scary. I've spoken to many non-webmasters about it recently, from all walks of life, and not one of them knows that their search results are tailored towards what Google already knows about them and what Google thinks they want to know.

I worry about the implications for my teenagers. If they ever get off Facebook and try a Google search for something, will they be pushed towards (without being aware of it) the narrow range of sites that their friends visit? What if they want to break away from their peer group? What happens as they grow up and start wanting more sophisticated searching - will Google grow up with them or will it continue to base what it shows them on what they looked at last month and last year? What if they click on something stupid at 15 - and get "judged" by it and haunted by it for months afterwards? What if they are doing research on Nazis for a history or politics project and get marked down as having extreme right wing inclinations?

I've recently come up against this "narrowing" of results myself. Every year at this time I search for about 30 interesting videos around a particular theme. In previous years it has been a joy to do this, and I am often surprised and intrigued by what I discover. This year it seems that the millions of videos available on YouTube have been shrunk to only about 250 available to me - I am going round and round in circles and being shown the same videos over and over again, no matter what variations of keywords that I type in. And yes, I get better results searching YouTube with Bing.

Finally, I have to say that I get very peed off when Google thinks it knows what I want better than I know it myself. I have my own brain, thank you, and I'm perfectly able to use it. I don't want my searches to be limited to the sites that I clicked on last week, or that my "social network" +1, or that my postcode suggests that I might be predisposed to. Google used to allow me to explore all sorts of sites, all over the world, good and bad, interesting or dull, heavily ad-laden or ad-less, and let me make up my own mind what I thought of them. That's why I loved Google and made it the search engine of my choice.

@SmallP, what you said. You've said it much better than I could. I would say you've made some very interesting and relevant points. I'm sure the official response would be something like, "err", "um"...