I'm More fan of AMD+NVIDIA but ATI have better support for Linux based OSes. That configuration was more to demonstrate I wanna kickass second to none computer. :P
As for computers I never really had a good one if we don't count a workstation which I never tuched back in 90's. My current oldie is ragged down low spec low performance computer machine which I tuned as much as specs allow. Build with lower middle class HW back in 07 this guy have problems playing 10-bit 720p videos and I can forget about 1080 completely.
Yet because I instaled 512MB GPU I can afford to play some never games like I played Assasin's Creed 1 or I sometimes turn on Star Trek online (even on low detail if not in combat or mission). But it's kinda sad because I can't enjoy so many cool games.
EDIT:
My PC:
AMD Sempron 3000+ Manila core 90nm architecture 1,61 GHz 800 MHz bus
4GB 800 MHz DDR2 RAM (bought myself as part of upgrade)
MSI MS-7309
GeForce 9500 GT 512MB Asus
PSU EVOLVE Pulse 400W