Actually, you can get pretty good performance with a gaming laptop now a days without spending an arm and a leg.
In my situation, I needed a laptop for business but couldn't afford another system for gaming.
On some good advice, purchased an ASUS G73jh series laptop for about $1700 with tax. It's has a 17" screen,
full size keyboard (important), intel i7 core (Q840), ATI 58xx vid card, with 8gig ram running Win7.
I can run RoF full settings. CLoD full settings (London screams to a halt though), DCS A-10 full settings (textures
and water turned down a notch though). Falcon 4 w/BMS full settings. All these with FPS in the 30's.
I know a desktop will give better performance, but don't think you can't have fun running flightsims on a
laptop either.