See my earlier (possibly related?) post on an inability to upgrade to WordPress 2.8.
It looked as though my laziness in tracing the upgrade initialization problems had caught up with me earlier, as I found I was unable to edit existing posts or pages, with a blank white page being presented, and no changes committed since using 2.8. Deciding this wasn’t something with I’d just ignore for now, I went through the plugins, individually disabling them, trying to edit an existing page§. If the page updated correctly, with no blank response, I re-enabled the plugin, and disabled the next in the list. Of course, I didn’t find the misbehaving plugin until the second to last one – WP Security Scan. I’ve left a thread informing the author on his forum, and just left the plugin disabled for now.
§ – In case you’re interested, I noticed that either the newer version of the DandyID plugin, or a change in WP2.8 had caused the list of places you can find me online to be presented on seperate lines, with accompanying text, rather than the space saving row of icons I had previously. This information has now been moved to the About / Contact Me page.