In my experience, the thing people have most trouble with using Subversion is moving directories around. They expect to be able to open up the Finder (on OS X) and drag a folder somewhere else - but doing so without using "svn move" results in massive confusion later on as the hidden .svn directory gets moved at the same time, breaking things.

Many (all?) distributed systems solve this issue by keeping repository metadata in one place at the root of the project rather than spreading it around in lots of .svn folders.