I have been coding a bit on a Zenphoto plugin the last couple of days, it is a sitemap generator which can be used with the larger search engines (Google, Live Search, etc.) and it's compatible with the sitemaps.org specifications.
It's really simple to install, just copy the file into the zp-core/plugins directory, activate the plugin through the administration interface and then point the search engines at [your Zenphoto folder]/?sitemap, and it will take care of the rest.
Link for download and (a little) more info is on my homepage.
Note: I am aware that there is an existing Google sitemap generator already, which is mentioned on the hacks page. But I haven't been able to access the site linked to recently, and now that I have seen the code it honestly isn't that pretty made.
By the way... Shouldn't there be a plugins section here on the forums, in order to keep them a bit separated from the Zenphoto core?