These are some of the problems most likely to annoy new users:
If an svn client is directly accessing a repository via a file:/// url and is interrupted, or crashes, (or if httpd crashes), the repository is likely to be left in a 'wedged' state. You'll need to run 'svnadmin recover /path/to/repos' to unwedge the repository. Make sure you shut down httpd before doing this.
See Issue #739 and http://subversion.tigris.org/project_faq.html#wedged-repos for more details.
If Subversion cannot convert log data to your local charset encoding, it will (currently) just show "[unconvertible data]" for the entire unconverted log message. This is lossier than necessary. There are even some revisions in the Subversion repository itself that exhibit this behavior when the client locale is ISO-8859-1 (Latin-1).
See Issue #807 for more details.