I'm mostly a PC user, but when I needed a laptop a couple of years ago I ended up buying an iBook G4 and on the whole don't regret it.
Pros are the near-instantaneous access when I open the lid, the reliability, and very good stability.
Cons are software incompatibility with the PCs, much more restricted range of games, and less compatibility with some types of external hardware; for example I wanted a microscope camera and because of the way I'm set up it would mostly be used on the laptop - I could get any of a dozen models around £50-100 for the PC, the cheapest Mac compatible is several hundred pounds. Keyboards are another example - there are hundreds available for PCs, virtually none other than Apples' own for Macs.
There's a Mac version of Microsoft office, but it's nowhere near as good as the PC version - no idea why, it just isn't. But Open Office is Microsoft Office compatible, free, and better, and there are versions for just about every platform including Mac, Linux, and PC.
The only serious problem I have, and it's probably only noticeable to someone who lays out VERY large documents in e.g. Word or Open Office Writer, is that the way fonts are handled differs slightly between the PC and the Mac; after several pages the page and column breaks in documents will be in slightly different places, and things such as text boxes may suddenly shift from one page to another. It sounds trivial, but the last book I worked on was nearly 100 pages of double-column text with lots of illustrations, text boxes, etc., and every time I worked on it on the iBook I had to accept that I couldn't lay it out with any accuracy, since everything would be changed when I got it back on the PC.
