iPhone and iPad users running the latest version of the iOS shall be glad to know that a tethered jailbreaking solution from the Chronic Dev Team should be up and running very shortly. GreenPois0n, as it is called, is based on the Limera1n exploit that was uncovered by George Hotz and is capable of jailbreaking all the iOS-based devices in the market.
One problem however is that this shall be a tethered jailbreak. This means that you should tether your iDevice to a computer every time you need to reboot in order to keep the jailbreak active. If you think that is a pain you can live without, then you should probably wait for some more time before an untethered jailbreak solution is made available.
But again, there is no need to wait if you have an iPhone 3G or a 3GS running the older bootrom. The RedSn0w 0.9.6b3 update that was released last week for the GM build of iOS 4.2 is good enough for these devices.