BTW, I added the swipe up and down to my sourcecode. I also remapped the default left and right gestures to suit my needs.
For me, swiping up and down on my iPad while a movie is playing skips 10 mins. And swiping left and right can be mapped to fastfwd/rewind or skipping 30s forward/back. Each of these gestures does something else entirely when not playing a movie.
Changing behavior for left and right swiping is probably easiest for regular users because it's simply adding a keyboard.xml keymap to /var/mobile/Library/Preferences/xbmc/addon/keymap
There's a lot of instructions or threads on the forum already about how to customize these keymap files.
I believe swipe left is currently mapped to "backspace" and right is currently mapped to the "tab" key.
Remap those keys to anything you like under the <FullScreenVideo> section. FullScreenVideo section is used when a video is playing in fullscreen.
Sorry, I don't currently have the time to write a full tutorial. I have added plenty of info to the apple remote threads in the past and the basic concept is the same. So search for those post for help.
I am sure once the XBMC developers get more touch screen devices in their hands, they'll be able to figure out the best implementation for touch gesture. Please help them there if you haven't already. If every XBMC user donated a dollar, more hardware can be purchase so the developers can program against.
http://xbmc.org/contribute/donate/