I jailbroke my iPhone yesterday. I used blackra1n and have installed both the Cydia and the Rock APT installers. I've got mine turbocharged now (even got a bittorrent client & webserver running on it!)
It's really quite amazing how much it opens the phone up. It was a nice product before, but this makes it no different than running a beautiful, robust little multi-touch UNIX computer in the palm of your hand.
I don't know why I was so previously opposed to jailbreaking and was so embarrassingly far off. This device is head and shoulders above anything out there. (All Android devices included in that not-so-humble assessment) Unlocking the file system on the phone & providing a means to install 3rd party software on it outside of the AppStore (which is all that jailbreaking really is) is a no brainer and totally enhances the experience of owning this device.