Had some trouble getting my subversion to work, so I thought I would post about it here. I've had a good time setting up my new Dreamhost account, and have followed various tutorials in the wiki and forums, so it's hard to say whether my changes caused the problems - but I doubt it.
After setting up my svn repository on a new domain (svn.domain.com/svn) - I found I was unable to checkout, both remotely using TortoiseSVN and logged in via SSH. Taking a look at the apache error log showed:
ModSecurity: Output filter: Response error too large
and was producing a 500 error.
Looking into the problem further, I found that it was being caused by mod_security and tried to disable using .htaccess (SecOutputFilter Off). I must have gotten that wrong because that stopped me from being able to access the repository at all. Searching the wiki for mod security showed that enabling "Extra web security" when setting up your domain turns on mod-security.
Sure enough, turning off "Extra web security" in the Dreamhost panel and waiting for the changes to come into effect gave me full access to my repository.
I'm posting here to see if anyone has any further information to share, and perhaps someone can amend the Subversion installation instructions to help if someone else runs into this problem.