I’ve done this to myself a few times. After I hit commit I realize I need to cancel. Unfortunately these usually leaves the local subversion copy with a lock, preventing subsequent commits. The message is something along the lines of:

Error: svn: E155004 Commit failed (details follow):
svn: E155004: Working copy '/path/to/repo' locked
svn: E155004: '/path/to/repo' is already locked.

Frustrating.

I used to fix this by deleting the lock file with a command like this:

find . -name 'lock' -exec rm -v {} \;

The problem is that with Subversion 1.7 this doesn’t work anymore. The good news is there is a better way to do this - and what it appears I should have been doing this all along. All you need is:

svn cleanup

If you’re interested, the man page is available in the SVN book.