Got my XFX 6800 Ultra yesterday! I'm so happy. Anyway I want to know why NVidia are freaking out about this cards power requirements, cuz they say it must be either a 350, 450, or 480W PSU (different sources, all lead to NVidia, though

) Anyway I'm running my card on a 300W Freetech power supply and it's doing fine, so I just want to know why they make such a big thing out of it? Are they just
trying to make you spend more money on a potent PSU
on top of the money you just spent on the card?
Needless to say, I'm don't feel
entirely safe running it this way, but due to unforseen circumstances (lol) I had to end up using it instead of a 480W PSU which my dad must use so he can power his SATA hard drive. Will I be ok? If I get a new PSU will I see any increase in performance? I'm upgrading my computer
very slowly so maybe I'll save up, get a 400W Zalman PSU, and get that out of the way.

What do you guys think I should do?