My dev machine at work is a total processing monster. I can feel the difference there, cause I have a ton of windows open, I am compiling code, I have multiple database instances open all running queries.
While it is not running like this all of the time, it is nice when to know that I CAN do all of this at the same time without having to worry about the machine not being responsive.
My two home machines, however, are a 700mhz TBird and an 850mhz P3. These are just fine for me at home.