Steam already has a favorites list. Just put whatever you're playing right now up there.
Thanks for the deal, OP. I may have to pick this back up to get ready for # 2.
A favorites list isn't true organizational ability. That's a single divider, and which games lie on which side of it must be manually decided. Plus, steam's text is tiny and hard to read, even with a small selection of favorites, it's somewhat difficult to tell them apart. Would it be so hard for them to deliver a traditional desktop functionality, or even something like the Xbox 360 Arcade?
Plus, they already have all the games categorized in their store by publisher, developer, and genre (which is a very handy feature btw), why not allow us to apply the same organization to the games list?
Another nitpick, steam is pretty sluggish for a 2d app. Try dragging the steam window around, it's just not as fluid as it could be, possibly because they implemented their own GUI instead of just using Microsoft's built in stuff. And the steam overlay is very sluggish, though Valve blames that on their use of Internet Explorer and how poorly suited it is to that type of integration. I believe their implementation of the Steam overlay is basically just taking a framebuffer snap shot and then overlaying it on top of everything. They've considered switching to webkit, but considering that there's been no major improvements to Steam since it's launch in 2004, I doubt we'll see anything anytime soon.