First of all, Leo says he prefers gaming with a desktop that he can put an actual card in. There's sacrifices that are made with a laptop. Since Scott is on the road a lot, a laptop is necessary though.
Leo says that video RAM is used for textures, so games like flight sims or shooters that require real-time graphics require higher end graphics chips. The more memory he gets, the more elaborate textures he can have. Frame rate and responsiveness is the key, though. A faster card with less memory would probably be better for him for the better frame rate. He can compare reviews at AnandTech and PC Perspectives and they'll give him a hint of what's best.