10-16-2009, 12:50 PM
The more you have running in the background slows it down, jailbreaking gives you a app to control what runs in the background, and instead of just exiting an app you can actually kill the process, among other things. I noticed that jailbreaking might give a bit worse battery life (or it might be that I used mine a lot more) and slows it down a little (nothing major) but it is worth it when you can get (mostly) any app for free as well as things not supported by apple.