Don't think this one's documented in the manual...
Also, i don't have a touch and only saw this vid on YouTube, which i can't find anymore..
Anyway, here it is.. when typing, hold your finger on the delete key and while still holding, drag left on the screen to delete multiple characters, if you delete too many just drag back in the opposite direction and the delete will be undone.
Haven't had a chance to try this one for myself, so let me know how it goes.
EDIT:
Sorry, just found the Video.. Here's a link: Delete Feature
Also, i came across this video, not really a tip, more of a bug, but maybe someone will be able to put it to good use: Link
Basically a way to rotate photos...
both excellent, thanks!