Thanks csdude55, I doubt it's related to fewer searches, although that could also become a trend.
I wonder if it's to do with people having no need to search for facebook, as they already know it, and the fact that many more are using a facebook app. This cuts out the need to use search for such a "destination."

There are lots of sites that i don't search for anymore because i already have them loaded in my device. Imho, if there is actually an increase in searches like we are told, it is mostly for trivia.

It could be related to the FB app, but if I understand correctly, that came out in 2007. Why would it have a sudden impact 6 years later; specifically, June 2013?

Further, I know that with my own Search Analytics (from Webmaster Tools), I had about 30,000 clicks in the last 30 days from people searching for my company name minus the .com (which I assume are people that don't quite grasp how to use the address bar). I would assume that Facebook users are just as unsavvy as my own users (probably less).

If the trend is really irrelevant, though, then it makes me question what data we, as designers, CAN rely on? Facebook can make whatever claims they want on traffic and number of users, but from my own experience as an advertiser there, I believe that a lot of it either comes from robots or is simply fake (I get emails every day offering to sell me thousands of "likes" from fake accounts). So if you can't trust Trends, and you can't trust their own numbers, what can you trust?

Remember that Google Trends shows relative volume - so, if search queries diversify, this is at the expense of other queries. It doesn't show the total search volume.

Is that also true for Google Trends > Topics? I'm of the understanding that it includes all queries that might relate to Facebook, too.

Yes. Here's Google's help on the subject:

The numbers that appear show total searches for a term relative to the total number of searches done on Google over time. A line trending downward means that a search term's relative popularity is decreasing. But that doesn’t necessarily mean the total number of searches for that term is decreasing. It just means its popularity is decreasing compared to other searches.

[support.google.com...]