WebOS is unique in having the 'ripple' reticle whenever the screen is touched - it's really useful feedback to show the user that the device is doing what they expect it to do.
I know that Palm are currently implementing hardware acceleration into the UI, and I think that they should consider my idea of showing a trail when the user swipes or drags on the screen.
As long as it is hardware accelerated it shouldn't take up too much system resources - and it will add a layer of interaction and visual feedback that is not currently offered (that I know of) by any mobile operating system.
Plus, it'd be fun to just play with - don't underestimate the power of doodling, people would love it
Here's a simple little mockup to explain what I'm talking about. What are all of your initial reactions? Love it or hate it?