well really i think we need to determine why the native scaler doesnt work for all of us, even when we're at the native resolution. that still sounds like a driver problem to me and this is just a temporary fix.
as for the performance implications, i couldn't say. my box is an old nintendo cartridge slot A athlon and everything seems slow to me these days. I can play fullscreen dvd with no slowdown with mplayer though.
someone with time ir their hands should benchmark it :P