on my edgy install i use two debian ,1 fiesty,and a picassa and swiftfox repo's
i have had no breakages.but i do have an on going sound issue with edgy,but it seems that the bug is not important enough to be fixed yet.

feisty got brocken with the updates the other day,dont know why but after the updates x failed to start,

those that say it changes your source list,i have only seen it add its repo's that it uses, and if it does stuff them up they are a lot easier to fix ,than trying to fix xserver after trying to get the resolution sorted..