I've tried gimp before I got PS. I didn't understand it at all. It had a very confusing layout. For a free program it's ok, but I much prefer PS. As to being just as powerful, I highly doubt it. CS3 can take a 2D image and make a 3D layout from it (I don't know how to do, never took the time to learn, but I've seen my friend do it).
I'm sure there are ppl who can create amazing things w/ gimp.