I have a 2.33GHz MBP and it's plenty fast! I've only used the Imacs in the store, but from what I can tell they're not leagues faster. Memory is probably a much greater contributor to overall performace on these machines than processor speed. Get the machine that best suits your needs, max out the memory and you should be happy for a very long time.
If you're a student or an educator don't forget to use your school discount, could get you 10% or more off your purchase price.
Oh, and one onther tip.... Buy on or after October 26th. The latest version of OSX (Leopard) is due out on that day, and if you buy a new machine after that it will come with the new OS.