I don't know why it took me so long to discover the conflict, but Wordpress' Lightbox and PicLens plug-ins don't work so well together. When both installed, PicLens works, but Lightbox freezes if you try to navigate to another image while one is already displayed. I put out a cry for help using Twitter, and Cor Bosman wrote back with the answer. It was in Cor's best interest to figure out the problem, anyway, because he's using a similar system. :)
To fix the problem, we just renamed all instances of "pause" in lightbox-2's lightbox.js to something else.