If your gallery 2 install is occasionally getting hammered by search engine bots, the culprit is very likely gallery’s slideshow- search engine bots seem to get trapped in it, and hammer it badly- sapping both bandwidth and CPU (since it hits mysql a lot.)
To deal with it, either disable the slideshow module via the control panel, or use robots.txt to block bots from hitting the slideshows.
This information is surprisingly difficult to find, so I post it here for posterity and for Our New Spidering Overlords.
(Ob. developer/development tangent: it is pretty mindboggling that the gallery developers haven’t figured this out and either made the slideshow bot-friendlier or disabled it by default. I shudder to think what this is doing to people- my load was regularly hitting 18-20 and requiring apache restarts until I figured this out; has hardly crossed 0.1 since then. Thanks to the fine folks at rimuhosting for not throwing me off my shared host before I figured out the solution to this problem ;)