The iPhone Dev team released a new tool called QuickPwn that jailbreaks an iPhone more quickly without requiring a full restore.
The released QuickPwn version is still a development version and only available for the Windows platform right now.

Currently QuickPwn requires your iPhone to be running version 2.0.1 of the iPhone/iPod firmware. A full release version of QuickPwn is expected in a couple of weeks.
More details and download of QuickPwn available on the iPhone Dev Team site.