If you’re looking for information on adoption of a given platform, framework, or JavaScript library,BuiltWithhas a nice site with tools and reports for that. You can view pie charts of current distribution:

or view trends over the last year (or longer with a paid account). For instance,here’s the trend chart for ASP.NET.

You can also use Builtwith to inspect how a given site is built, and what kind of libraries it’s using. For instance, the weeklyASP.NET community standup site,live.asp.net, is built with:

I haven’t tried the paid features of the site, but I’ve found the free resources useful. Let me know if you’re a paying customer what you think, or if you have other similar sites you recommend.