I have been playing SSF4AE on Xbox and have been wanting to get it for PC for a while now. With the 20% off code it is the best price I have ever seen it. It looks and runs great on my Win7, AMD Phenom II 965 with 8GB RAM and a Radeon HD 6950.
I have not played online yet with the PC version. From what I understand it is not like Live where most of the people left playing are the hardcore fighting game players. Which suits me fine.
The PC version of AE is great. I've probably put over 500 hours across the various console iterations of SFIV. Bought it on a whim a few steam sales ago and haven't looked back. My machine is probably mid level at best, yet it still runs flawlessly on the highest settings. It is a small, but noticeable improvement over the 360 version.
I do agree that the online competition is a few steps below that of Xbox Live, but you still run into some pretty good players. I did have an issue with GWFL acting up and deleting my save data. Didn't lose my battle/player points, but it did wipe everything else (unlocks, achievement progress, etc.). Only happened one time in ~100 hours of play so I may have just been unlucky.
$8 is an amazing price for this game.