Laptops are heavy, touchpads are a horror for even the simplest Flash game, even after 2 years constant working with it (7+ hours a day). Laptop keyboards are bliss, though.
And a laptop isn't comfortable on your lap, trust me. I've had to try it when I was in class and we ran out of tables, no fun.
Also, watching DVD's is only half fun, since most laptops don't have surround sound, and once again, not all that confortable.
A PSP would be good for a lot of things, but what I'd really go for is a Flybook like item, a laptop the size of an A5 sheet of paper. Just enough keyboard to type on with 10 fingers, and small enough to fit in my coatpocket. (Big coat, big pockets, though.) And 7 hours of battery life.