I currently own a good gaming PC, PS3, and a Wii. They cover almost all bases, so I've never felt I needed to get a 360. I play most of the 360 'exclusives' I want (but looking and sounding better, and far cheaper, with better online options), I have a gamertag, and I even use a 360 controller on the PC for many games; the PS3 and Wii gets me pretty much everything else. There is only one exclusive game on 360 that I'd like to play and that's Fable 2, and I'm still not convinced that won't come to PC at some point.
So, given the 360 currently has no games I really want to play, for it to be an attractive option the following would need to be in place:
1) £99
2) No online fees, like Live for Windows
3) Confirmed reliability
I almost have the first, do not have the second, and do not have the third.
I also have a PSP and an iPod Touch. Both serve my needs well, but there are many games on the DS that appeal. But I hardly play handhelds nowadays, so the only reason I'd buy a DS would be, well, if I was given one for free.