Perhaps if you bike is not running right. Mine runs fine so I would not consider a Power Commander. I can see this thread being re-posted Never-Ending Pointless Recurring Threads.
I put one on my 09, mainly to richen up the fuel mixture. I feel the California bikes run to lean. That being said, it did richen it up, and it it improved start up, as well as throttle response.
I put one on my 03 but only because I got it at dealer cost and the instalation and custom dyno mapping was free :yahoo: . It did make it better at low speed and with the custom mapping I didn't lose fuel economy.
I think it depends on a few things, the main two being 1.) how you ride and 2.) if you have ever had a bike with perfect throttle response. If you don't do a lot of twisty road riding, where you are rolling the throttle open and closed a lot (leaned well over), it might not matter. #2 is really just the "don't know what you are missing" component. I learned how to ride around the snatchiness that was in my bike's throttle, and got pretty good at it. Now I don't have to.
That being said, if I mostly did touring- or was one of the guys who expected to get 10k miles out of a set of tires, rather than 4500, I wouldn't bother. You will lose some mileage, which may not be worth it to you.