That's a tough one, but a great question.

It has to focus on the specialities of the small business that the big business can't do.

Big business is big for all kinds of reasons, but most often because it's cheaper. It cannot usually offer the same "service" of a small provider. That can apply in the online world, too.

The nearest comparison I can think of was a friend that set up his business with key differentiators, and that was service and support.
I heard him on the phone to people that if they wanted to buy it cheaper, there are dozens of suppliers, and he always named the big ones that he knew he couldn't beat on price. In fact, he'd often give out their phone number.
Essentially, what he said was, by paying a little more the customer would get free support to setup the system. He added, if they were within XX miles he'd arrange for an engineer to call and set it up for them. In the vast majority of times he won the deal. He didn't tend to win the big orders which were purely down to the lowest price.
He knew his place in the market, and he never strayed from it.

I guess you could find parallels in other sectors where it's about offering something the big outfit cannot do.

I would think that quality, then service would be the most important things for people. Price would often come behind those, even if it was measured in more detail.

Is that the kind of thing you were thinking of?

Your friend provided a good customer service, but he was smart enough not to give it all away to the public. He supported those who asked him for advice or support. However, he wouldn't provide all this information about his competitors, a map with a direction to them, or a free shuttle bus by default/in advance to the public. If he did, many of those who would potentially ask him a question, would take advantage of his free directions / free shuttle bus, and he wouldn't even have a chance to introduce himself to his potential customers.

The same thing may be with webmasters who promote the big brands and link to those big brands (which are their direct competition), for free. Those webmasters who put Adsense links at least make some money from their visitors getting redirected to their competition, but those who freely promote their big competition may not be in the best position down the road. Actually, it's probably too late because the big sites have already eaten their lunch and those users, unless something unexpected happens, aren't going back. They have more choices, more speed, more people on Facebook than on your own forum or blog. One would think - "but you should do what's best to your visitors, no matter what." Well, in that case, since you are never going to win with a big competition like Facebook, you may be right. Sarcastically speaking:

1. Build and promote your own website.

2. Realize your website and offer is not as good as Facebook's.

3. ("Do what's best to your visitors") - Find the best landing page, Facebook group, etc. on Facebook and forward all your visitors to them.

4. Close your website, keep paying off your debts, and have a satisfaction that your visitors have now the best experience that you would never be able to provide them anyway.

But, wait, if you take the example of Facebook, there's absolutely nothing there that's private. People post so much personal information, and I look at that and think, wake up and smell the coffee.

The differentiator is that the smaller online sites can provide that anonymity.

If you refer to Amazon, well, yes, it has grown to become a brand, just as Facebook has, and it's probably too late for many to get in on the act. These are destinations. However, there are many smaller businesses that are offering niche products and services. Getting airtime is the challenge. The eternal need to get to the top of the SERPs.

Yes, the free shuttle bus is a little over the top, imho.

Sites like Facebook, Amazon are like big cruise ships. They have everything, 24/7 - that's why there will always be plenty people there. Small niche sites are like small boats that (by having promoted the big ships for years, for free) give a ride to these big ships. In the end, the big ships will have their own free shuttle boats (they already have) that would give free rides from anywhere to these big ships. Eventually, the small boats (small online businesses or communities) will not be needed at all.

What to do? What to do? Head spinning, etc.

Actually, what you do is provide customer service the big sites can't. They could, but only by taking a hit to the bottom line. Brands are about moving product, and people, Through their locations. Small business is about developing a long term relationship with the visitor/customer.

When I'm dealing with folks I do remind them they can get it cheaper at x, but I can do the hand holding and turnkey they can't do. And if it is local sales then do it in their office, home or other location.