I'm super excited about this little guy. I did a similar thing internally for just performance comments and it never caught on. Making all the docs there commentable is a stroke of genius. Not to mention a lot of rolling up the sleeves and getting that content out there.
Congrats and great job to the msdnwiki folks!
I'm already starting to add some class specific comments like this one from my old stuff and I plan to add more. It's a great place to park thoughts so they don't get lost.