I’m updating my server from SVN almost every single day, and while this had sometimes broken my environment in the past, I didn’t have any problems in the last few weeks.
Given the many different possible setup and configuration options, this doesn’t necessarily mean anything. It could be that you are using something that I don’t, and it is that which makes the difference.
In any case, I would recommend using the -r##### option of the svn update command to progressively update, revision by revision, until you find the one that breaks your setup.
Also try to provide a bit more details about your environment here. What revision are you running now, that still works? What version of PHP are you running? Any special thing about your setup: LDAP integration, SSL, …
It appears a bit strange to me that there’s nothing in the apache error log.