I'm getting some lag on Portal when graphics are maxed. I'm thinking my GPU is the bottleneck here, but here are the specs:
8 GB 1333 MHz DDR3 RAM
Intel Core i7 740 QM
ATI Mobility Radeon HD 5650 1 GB GDDR3
500 GB 7200 RPM HDD
1920x1080 OLED multi-touch LCD
Also, it gets pretty hot when I'm running like this. My laptop is barely thicker than a netbook which makes me wonder if a more powerful GPU will even fit in there.