Hopefully this info will be useful to someone having the blank page problem:
I was having the "blank page" problem sitewide. I could not view the site or log into the dashboard. I run WP 2.7.1 and PHP 5.2.8. I read this thread along with several others and I ended up going into the WordPress database using PHPMyAdmin to disable my plug-ins by hand. Under the wp_options table there is an "active_plugins" entry which you can edit in order to disable plugins without having access to the dashboard. If you look at the structure of the list of plugins you'll see how much text to delete in order to disable them.
It would probably be a good idea to back up your entire database before attempting any of this, BTW.
After I edited and saved the entry in PHPMyAdmin, the blank pages went away and the site loaded fine, as well as the admin side. You can then re-activate plug-ins one by one to see where the problem is. In my case it was very strange... I'm currently still building the site so it's not public yet, so nobody had been on it. One day it worked fine, then I didn't even touch it that evening, and the next morning the blank pages had invaded. If it was indeed a bad plugin, I'm not sure what activated it or caused it to start making trouble.
But anyway, <phew>... crisis averted. My thanks to all the participants on this forum for their good documentation of these errors.