it really is just down to games really. i got someone to buy a macbook, a white one, and he said it's the fastest computer he's ever used. he can't get over just how fast it it is (1.83ghz)...
the shared graphics are still relatively powerful, but not full half-life2/doom3 with-all-the-options good is all. video encoding is almost totally down the processor. photoshop will run better on a macbook than virtually any other computer pretty much, other than a macbook pro... i would probably get the mac book. it's smaller, lighter, nicer and a lot cheaper.
Dual 1.8GHz G5 2GB, 1TB, Radeon 9600XT 128MB, 10.5
20" Apple Cinema Display + Dell 2005FPW 20" dual-head
iBook G3 700MHz 640MB, 40GB, Rage128 16MB, 10.4, dying battery