After upgrading to WP 2.8.1, several users were unable to view wp-admin. The page was completely blank.
After some investigation, the page would load up until it fetched the CSS file for the wp-comment-remix plugin, then hang and quit. After disabling this plugin, the wp-admin page now appears for those users.
If I have some time later today, I'll try to dig a little deeper and see if I can locate the problem in the page load.