I could get a Macbook really cheap so I didn't think twice and i've been using it for three months as a "render farm" (LOL) for Shake.
In rendering igood luckt is overall faster than my dual 2.0 G5 at home.
I also run Shake on it when travelling. With 1,25Gb Ram it runs smooth, no problem (only the tiny screen).
Dual screen with a spawned viewer at 1280*1024 and still no worries.
I agree with beaker the Intel 950 is plain crap, but Apple got the job done and it runs ok (although on XP it's unusable).
This is pretty basic, but please: make shure you are running shake 4.1 and the latest OSX!
and i agree with breno_speno that launching shake from the terminal is usually better (and alows you to have 2 shakes running).
good luck