I'm running Maya on a Dell Inspiron 8600 laptop, and everything runs really well. I've only had a couple of viewpanel refresh bugs, but I attribute that to video drivers and windows XP being a piece of cr*p.
Otherwise, things are nice and speedy on this machine.
It has a 1.7 GHz Pentium M, 1 GB RAM, a 15.4" widescreen at 1920x1200 resolution, and a 128 MB Radeon Mobility 9600 Pro Turbo video card. The laptop is about 7 lbs, so it's not exactly a lightweight box, but it's not too heavy to carry around on a regular basis. I also added a combo DVDRW/CDRW drive, 802.11 b/g wireless networking, and bluetooth. Total cost of the machine was just over $3000.