In case you don't want to leave your Palm OS apps behind when the Pre debuts, Motion Apps makes a Palm OS emulator for the Palm Pre. The guys over at PhoneScoop got their hands on the emulator and have put together a little demo video.
The emulator looks amazingly good. Palm OS apps can be installed by hooking up the Pre as a mass storage device, then dragging the .prc files over to the Pre to an application called Classic Apps. Once it's in Classic Apps it just comes up in the emulator.