I had the same problem. Public page and admin page got blank after automatic upgrade to 2.8. I tried to manually upgrade after that without success.
I did view the source of the white pages and got more error information that lead me to the mo.php file.
I found out that it had something to do with the translation script in /wp-includes/pomo/mo.php.
Since my page had translationfiles for swedish language set in the config.php file, I just deleted the language tags:
in config.php change from:
define ('WPLANG', 'sv_SE');
to
define ('WPLANG', '');
After that, the site works as it should but without the translation.
Might be an issue with the translation files though. I have to look into that.
This might give some of you a hint on how to solve the "white-pages" problem.
Cheers