This is certainly the oddest problem I've ever encountered with my self-hosted WordPress installation.
Whenever I activate the last plugin in the plugin list, then attempt to publish (or preview) a post/page, I receive a blank page. The changes do save to the database, but the generated page contains no code.
I first assumed that this was a conflict with WordTube plugin, because I reactivated all of my plugins one by one.
However, after I uninstalled the WordTube plugin, now the WordPress Backup Plugin causes the conflict. Since WordTube initially appeared last (alphabetically) prior to uninstallation, I assumed it was a normal plugin conflict.
Now, the admin functions correctly when WordPress Backup plugin is deactivated, but on activation, it causes the same problem.
I've searched Google and WordPress extensively and can't find any solution. I also reinstalled all of the core WordPress 2.8.4 files via FTP.