Although the iPhone/iTouch Dev team hasn't published a general jailbreak yet, the developer community is working hard and furious to make sure that your arrival will be pleasant when you get there. Today brings this marvelous SpringBoard patch from Nicholas "Drudge" Penree, NerveGas and Pumpkin. It allows you to add as many 3rd party applications to SpringBoard as you'd like and offers a kicking-new paging feature; notice the paging dots at the bottom of SpringBoard.
The trip1pogostick patch is available from Drudge's beta repository. To access it, you must jailbreak your iPhone and access this link from Mobile Safari.