I have put online a little JavaScript tool which allows (mass-) moving
of images between categories within commons through point-and-click
(no use of keyboard necessary;-)
I tested this on my local MediaWiki installation, where it worked
fine, but didn't stress-test it on commons yet. It can't damage
anything on commons, but it might not work under certain conditions at
the moment.
That said:
http://commons.wikimedia.org/wiki/MediaWiki_talk:Cat-a-lot.js
Awaiting critique and bug reports :-)
Magnus