Well, I didn't find out about ThankRavelDay until today, which is sorta later. So I'll take this chance to express publicly just how impressed I am by what Jess and Casey have done! I'm so glad they have put so much time and ingenuity into it.
If you aren't familiar with it, Ravelry is a knit and crochet community. That's very simplified, though. Ravelry's biggest strength is that virtually everything is interlinked! It has some really unique features, too. The best may be the forum radar: you can watch the new forum posts from all over the site pop up one after another on one page. It's fun.
The quality level of everything on Ravelry is very high. Jess and Casey have done an excellent job!