Yeah I don't see what is so great about it either. They are pretty much the same except one costs money for no reason and the PSN doesn't have a size-limit for the downloadable games so it gets better quality games. Also there are some really minor differences.
Looks like a sloppy, chunky, and less elegant XMB. Why didn't they put the selected bar in the middle so you can see the bars to the left? And the static avatars look like a saturday morning cartoon, they're almost an exact copy of the Miis. I hope this so called "upgrade" is optional. I like the blades better than this.
PC, but if your only choices are PS3 and 360 then... Which system do you have more friends that play COD4 on? Otherwise they are pretty much the same other than the different controllers and one is free to play online.