I'm using 8400M GS on my HP dv2580et laptop computer and I'm really pissed of the that card... I thought that this card was great for everything, I wasn't able to play Crysis even at the lowest rates.. But the worst thing that hurts me more than anything is that Compiz Fusion works very very slowly on the machine..
I tried some of the settings that are suggested on the forum and it's more usable now.. But a lot my friends that uses other cards (7600 or intel..) have better performances than me which really makes me mad..
I really wait for nVidia to solve such problems