i'm a designer, and i've made the switch to mac. i have the 12 inch G4. Its plenty fast but i'll probably end up getting a G5 desktop later on.
as far as the file compatibility, I havent had any problems with my adobe files between PC and MAC. but I've seen people with docs on SONY storage devices and they dont work on MACs.
whatever you do, dont get the regular MacBook. Plastic dont work too well for MAC when it comes to cooling.
I have friends with 15 and 17 power books, the battery life isnt that great on the 17 cuz of the huge ass screen. Also depends on your setting on the laptop. there's a better energy saving mode, in that mode I still get about 3-4 hrs on the battery. mind you i've had my laptop for almost 2 yrs.
Theres been a couple incidents of laptop battery explosions. DELL had like 3-4 and i've seen 2 for powerbooks. I dunno about DELL but the powerbooks had a recall a while ago and those ppl that exploded didnt do the recall.