[princessnatalie]

I have used both, Photoshop at school for all our Yearbook stuff and Gimp at home for personal use.
One thing I have noticed that Photoshop can do that Gimp cant is clip paths (or I just havent figured it out yet), which you may or may not care about, but for yearbook its wonderful. Clips are when you take a picture, cut the background out and just have the person, or whatever. Also, I agree with most of the people above, Gimp's userinterface is harder to work with than PS.
However, if you havent used either, it may not make a difference which program you choose.