Well just look at Doom3. Doom3 has 4 main levels of image quality.

Low
Medium
High
Ultra

Ultra can barely be used by todays cards even when they are overclocked. Newer, faster, bigger memory is needed to reliably run Doom3 in Ultra quality mode. And it's not even out yet. Just imagine what Half Life 2 might require... or what's next after each of them?

Oh, and I'm not getting one. I like my Matrox cards, but the Parhellia is just way too expensive for me. I might up to a P650 if I have some spare cache around in a few months.