[QUOTE=Michael D]And you may get lucky and find some of the harder to find titles there (I found Metal Slug 4 and 5 on Xbox for $9).
[/QUOTE]
*pops his collar*
I managed to score a NEW copy of Xbox MS4/5 from the local Pamida for....$7.

Anyway, back to the topic...I play my Xbox almost every single day, and I don't think that will change when I get a 360. Like previous posters said, you can get the games new for next to nothing, and they tend to be better than their GC/PS2 counterparts.
The hardware switchover period is always a boon for collectors, especially when consoles aren't backwards compatible. Everything gets marked down, and people pratically give their stuff away. I got my Xbox for Xmas of 05, and amassed about 10-20 games by August of 06; my collection currently stands at 134, with more coming every day. The most I've paid for an Xbox game was $30 for Ninja Gaiden Black back when I first got my Xbox. The most I've paid since then is $20 for budget games, but I usually pay less than that for new copies. Again, it's a good time for collectors.
Lately I've been playing compilation discs, such as Taito Legends, Midway Arcade Legends 1-3, etc. Shorter load times and native 4 player support trump the PS2 ports, plus they're cheap. I've also been working through Serious Sam II, and I'm about to play the Halos again before 3 comes out.