i just went through a couple hours of anguish because the upgrade process from 2.2.1 to 2.3 silently failed. The upgrade.php screen gives an empty page with the WP logo on it. After adding lots of trace statements to includes/upgrade.php i narrowed the problem down to one select statement, yet there were no errors in the log file.
the problem was that PHP itself was running out of ram because the memory_limit = 8M
was too low.
I propose that wordpress upgrade.php include a check and a warning if the limit is less than 16M. once i went to 16M, the upgrade script worked fine.