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 a post/page, I receive a blank page. I first assumed that it was a conflict with WordTube plugin, but after I uninstalled the plugin, now the WordPress Backup Plugin causes the conflict. Since WordTube appeared last (alphabetically) prior to uninstallation, I assumed it was a normal plugin conflict.
Now, the admin functions correctly when WordPress Backup 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.