Another excellent article from Matt Gemmell on product design:
Generally, the best products demonstrate choice rather than offering it. Wise choices made on your behalf before you were even aware of them. Good compromises, made so that you wouldn’t ever have to make bad ones. We have a word for that kind of constraint: optimisation.
Matt's article talks mainly about hardware product constraints, but the same rules apply to software products. A great app will provide the best implementation of the most useful features and no more. Too many features and options will make an application too complicated and painful to use.