Carl: Just curious, but have you looked at all the other games you could be playing on a PS2? There are TONS. Surely GTA isn't the only game you'd play on it. What other games do you like for the Xbox and Cube?
I agree, I just got a PS2 recently and am totally enjoying exclusive titles like GTA-Vice City and Devil May Cry, but I'm also having a good time catching up on all the great PS1 games I missed. EBgames usually has a good selection of used Playstation games for super cheap. I just got Syphon Filter for $4.99!!
If you already own X-Box and GC, it would seem that you are a pretty avid gamer, so why not complete the trifecta with a PS2. With all of the PS2 titles PLUS all the classic PS1 titles out there, I'm sure you could find enough games to justify the purchase. They can be had refurbished(at EBgames) or used (on eBay) for about $150. Seems like a no-brainer for a hardcore gamer. YMMV.
If I was a hardcore gamer I could easily justify owning a third console but that's no longer the case. Leisure time is hard to come by. As a matter of fact the Gamecube + Metroid was a Christmas present for my brother (aka roomate) and I haven't played it at all. The hour or so per day I used to spend playing video games has been taken over by my cable modem.
I don't really use my CPU for gaming. CPU gamers tend to complain about having to use a controller rather than mouse + keyboard to play and I'm just the opposite. I've always been a console gamer. Besides, my CPU is a few years old and would probably have a hard time running something like GTA without crashing.