Great! I just merged the theme manager into the main gargoyle package, with a few minor modifications (the theme is now set using uci config variable instead of via symlinks).
I'm not going to include the extra themes by default as the css (specifically the copies of internal.css) are large and on some routers with 4MB flash we're really getting near the limit of what can be squeezed onto them. I do need to look into minifying some of my rather verbose javascript... but that's a project for later.
However, as of the next release, if you upload an additional theme to the /www/themes directory and reboot, the theme manager will be available in the System section, so you can select the theme you want to use.
Eric/Cezary, you should put a place to download themes on the download page here or build in a mechanism in the firmware that will allow users to select and wget different themes within the web interface.