We have PS2 and XBox.... I prefer the Xbox and it has more than a few exclusive games which are worth it. Then again, I do most of my gaming on the pc as I favor FPS and RTS games over anything else.
My daughters never touch the XBox, but use the PS2 all the time... I think MS need to do some work in that regard, at least towards the 5 - 9 age group... On the other hand, unless my eldest is not wanting to play with my youngest, I never touch the PS2.
I'd not be too surprised to find many people have both systems for the same reasons. GC costs bugger all now, so I'm thinking that may find it's way under the tree this year;P