2 years ago when I built my pc people said that I'm crazy for getting a 430W PSU ... 300W was all I needed ...
now I can't buy a GTX 570 because my PSU is not strong enough and I need to buy a new PSU ...
people nowadays say 600W or 850W for SLI is more then plenty ... until at the end of the year when the 7000series ati releases or at the beginning next year the 600series nvidia releases ... then you are out of luck with a 600W PSU !
Don't go cheap with the PSU ... the good corsair ones have 7 (SEVEN) years of warrenty ... you don't want to buy a new one in one or two years again
plan for the future and get at least a 850W one or you will upgrade sooner than you would like to
the PSU and maybe case is one of the things you can/will take with you for the next one/two/three pc build(s)
