ProSwitcher for Jailbreak Brings Safari Pages, webOS Cards-style Multitasking UI to iPhone
If you're Jailbroken yet still frustrated that you can't move between iPhone apps as easily as you can web pages in Safari (or Palm webOS users can in card view), ProSwitcher [Free beta - Cydia] is something to consider.
A front end to Backgrounder, which enables multitasking on a Jailbroken iPhone or iPod touch, duplicates the "Pages" metaphor in MobileSafari, including swipe-able switching and X-icon closing, and for good measure adds in the swipe-up-to-close gesture from Palm's webOS "Cards" interface.
ProSwitcher is currently in free beta and available via Cydia at http://booleanmagic.com/repo. If you try it out, let us know how it works for you, and how badly you think Apple better add this in to iPhone 4.0!