[quote name='Apossum']I would add a lot to XBL, but more importantly, I'd take away the

ing advertisements for gold users. As soon as you sign in to Live, Doritos owns your dashboard.[/QUOTE]
Let's be realistic in the things you'd like to see change, though. Ads won't go anywhere anytime soon, because that affects revenue far more than, say, reorganizing something.
My biggest pet peeve w/ XBL involves unlock key "DLC" - those 108KB files that contain entire DDR songs, or a whole slew of levels for Godfather. But, again: revenue. We won't see that kind of DLC go away unless people don't buy it - and then they'd "force it" on users by adding unlock key "DLC" to a game where people show their thin skin and lack of willpower - a COD4, Halo 3, or Bioshock content, y'know?
Unlock keys piss me off more than anything else, but to be realistic, what I'd add to XBL is better organization of the marketplace. If I haven't picked up a game in a number of months (say Saint's Row or Dead Rising) and want to see what DLC has been added, wading through the crap to see what genuine in-game content (no trailers, walkthroughs, gamerpics, themes, or any assorted junk) has been added is such a

in' chore. That shouldn't be such a hard thing to do, right?
All Games->(Grouped by letter folder)->Game Title->4 subfolders: game content, game videos, themes/gamerpics, and one other just in case.