After working on HTTP Cache Control for ZP, I decided to try to bypass PHP processing altogether in an attempt to make ZP run as fast and light as a static website. I think I succeeded, albeit not in the most elegant manner. ^_^
http://www.tummblr.com/my-code/zenphoto-plugin-static-cache-control/
"[b]staticCacheControl[/b] is a plugin that caches (and optionally gzips) Zenphoto pages on the file system to minimize PHP execution, [b]making your dynamic image gallery run as fast and light on resources as a static website[/b].
No matter how well you optimize PHP processing through code optimizations, opcode and database query caching, a dynamic PHP application still can't beat the performance (speed/time, CPU/memory usage) of a website with the same content displayed using static HTML files. However, good luck updating thousands of static HTML pages by hand.

With [b]staticCacheControl[/b], you can have the best of both worlds.
[b]staticCacheControl[/b] automates the process of generating static HTML copies of your Zenphoto pages, redirecting visitors to these cached pages when possible, and also the validating/refreshing of the static cache when your Zenphoto pages change. Thus, you can enjoy the performance of static pages without the hassle of updating them manually.
This plugin is designed for use in the album.php, albumarchive.php, image.php, index.php of your theme. It can be used in conjunction with (after) [b]httpCacheControl[/b] for optimal results."
I wonder if I've gone overboard with my attempts at optimizing Zenphoto's performance since ZP's quite snappy on its own.

Oh well, I learned a LOT doing this.