This nice little patch from ubuntuforums.org (the first one, patch_solution1_mirrored.txt) against the stock uvcvideo driver fixes the upside-down issue with the U6S built-in webcam on Linux.
Don’t bother copy-and-pasting the patch from the forum. It won’t work. Grab a login at bugmenot.com and download the patch file from the bottom of the forum post instead.
In order to get it to work in Skype, I had to edit my ~/.Skype/*/config.xml as follows:
<Video> <Disable>0</Disable> </Video>
(Are you happy now, G., you crazy fook?)