Hey,
I'm new to ZenPhoto and I just installed it about a week ago. I love it!
The theme system is so easy, so I went ahead and designed my own.
Here it is: watchtheworld: grid
I'd appreciate your comments on improving it and I'll be releasing it as soon as I make a few more tweaks. It doesn't validate yet, but I'll fix it don't worry.
Looking forward to your feedback!
Love it, it's random and unique.
As an added bonus, if you release it, I can add it to the growing list of themes available on the wiki at http://www.zenphoto.org/trac/wiki/ZenphotoThemes
:)