I really liked a recent post by Alex Payne titled Switching Season. He says he gets an itch every year or so to go try something different, and I can sympathize. What he says at the end really resonates:
It’s about computer usage as a creative act, something that becomes harder and harder to experience the more proficient one gets with a computer.
I feel this way every once in a while too - It used to be fun just getting a computer to do something. Once you know enough about how it works and most of what you do is handled pretty smoothly, some of the fun goes out of it. The problem with high-quality free apps like Mail and Address Book is that they remove the motivation for people to tinker with new ways of using computers for the same old things.
This urge to tinker is pretty strong, at least for me, and I think it might be one reason why I'm not so excited about web and mobile (at least iPhone) programming. Both platforms have a lot going for them, but the barrier to tinkering with my data is high - sometimes I can't get my data out of a service, and if I want to write scripts to combine two web apps, where do they run?
For example, I've seen a lot of great things come from the community built around BibDesk's scripting interface, and if it were a web app, none of that would have happened.