well my bro has an acer and plays games like wow and says it runs fine
WoW graphics are around 2003 level though... Source games are generally much more complex.
I have an Acer laptop with craptastic integrated graphics chip and it plays MMOGs like Guild Wars and older FPS games like Call of Duty 1 with no problems, but it can't handle any Source game I tried with a decent frame rate. I ran 3DMark on it and the performance is around Geforce 4 levels, though it does support DX9 shaders unlike the GF4.
I stick to my desktop system for newer games and only play old ones on the laptop.