This is just the type of question that does not quite belong on stackoverflow and yet doesn't seem to quite make sense here either. We need a general question site to handle this type of question.
Typekit works great and there are some great websites that use it.
https://typekit.com/gallery?utm_source=typekit-blog&utm_medium=blog&utm_content=bggl110701&utm_campaign=gallery there are more I'm sure but having big popular websites using a particular technology or not is not a good basis for its use. You should pick the technology that fits your needs and your audience. That said typekit does have some caveats.
Its a good system for using @font-face, which can be achieved more cheaply with google fonts or a manual implementation. So thats one thing to think about.
Another is the high marketshare of windows XP which does not have font smoothing turned on by default. If you look at the typekit site on a computer running windows XP in default mode, you will see how nasty and jagged the fonts look. Now this is the typekit site itself, no where else would I hold typekit to a higher standard. The windows XP problem is not limited to any specific browser either, @font-face fonts will often be jagged in Chrome for XP worse than IE8 (which has some tricks to helping with font smoothing).
Here is a screen capture of the https://typekit.com/fonts/proxima-nova page. On the left is chrome OSX followed by IE8 and Chrome on XP. Proxima Nova looks pretty good, even with the jagged font smoothing, and depending on the font weight you pick. (if you see the original screen capture the font jaggedness is abit more apparent.).
In the end its a personal value judgement on the level of effort you want to put in, and how important typography and the way typography displays is to you.