In my personal caste, testing WP3.0 on my test blog (I'll wait a dozen days before applying WP3.0 to my "production" blog), I also had the white screen of death, possibly linked to SuperCache.
My solution, born out from various experiments : renaming the wp-content folder, loading the blog (admin or public won't matter), for a few pages. Of course there's an error, but at least, it works.
And then, I import back into the wp-content folder, first, just the template folder (it still works).
And then, at this point, the blog works again, with all plugins deactivated, but it's working again.
After this, it's the plugin reactivation game.
The lesson I took : the next time I perform a wordpress update, START BY DEACTIVATING ALL THE PLUGINS !