It took a while and an additional brain to figure out that OpenSuse will not install the package
php_mbstring by default.
If this is missing you can't open the start page on
http://nameofyourserver/index.php (just a plain white page instead)
Mark, maybe this could be an entry in the upcoming installation guide?
I don't know if other distributions have the same "problem".
For troubleshooting: the apache error log pointed to the session.php in line 511 where strtolower caused the error because of the missing php_mbstring package.