You may or may not know about Google Trends. It's, in short, a neat tool that lets you see the trends in Google search. And it just occurred to me that it is a much more reliable alternative to a lot of statistics on the web.
When users search for a word, they are interested by it in a way or another. It means they know or want to know (more) about the search item, for one.

First example, using trends as a replacement to Alexa. Let's take the example of WoWWiki and Thottbot. And now, lets compare the Alexa results to the trends. Scarily similar for two totally different stats, no? Well, if you think about it for over 3 seconds you think it's totally normal. Not even mentioning the fact that a lot of browsers do a Google Lucky Search when only a word is typed in the URL bar.

Second example is Firefox and Internet Explorer. Understandably, Firefox is well over IE. It does not mean it is more used, but that users are more interested in it than they are in IE. A lot of IE users are users who don't visit the web a lot, and don't often search Google - or got no reason to. Let's not forget the default search engine is MSN Live Search on Internet Explorer 7+.

Now, I'm definitely not saying trends are accurate. Users search Google more than once on the same subject. Not everyone uses Google. People mistype words, abbreviate them... But it's still a very good insight into popularity comparisons. Remember there are millions of searches every day.