I prefer perfect binding for the look and when I'm busy working on a project and want to take a quick look at another product for reference or inspiration, being able to grab it off the shelf is alot quicker and easier if I am looking for a perfect bound over a saddle stitched...
however, a few years ago I lost a couple of saddle stitched books due to humidity or something... the glue gummed up and gave way.... the worse of these that suffered was from a company that makes generic rpg sourcebooks, that's all I'll say for fear of being flamed, but for some reason their glue didn't hold well at all under such conditions...
so far, however, all of my d20 books have held up that I'm aware of at least....with the books from WOTC and Mystic Eye Games probably having the worst of the exposure to the heat and elements (as I was carrying them around more)...