So, now that I've had some REAL experience dealing with Steam, my feelings about them have changed.
You are required to use their Valve application (aka Steam Client), which is basically a combination of game manager and browser for the entire Steam site. If you've got a fast computer, it's actually great! Updates to your games and the GM are automatic, but you can PAUSE your downloads and updates at any time! It's intuitive and easy to manage your games.
If you like achievements, you'll love dealing with Steam, as it has achievements for (I think) every game. It's easy to track your progress through the GM, which is always a nice thing
The downside of Steam is that if you have a slower computer, Valve will slow it down even more