I recently had to revert a svn commit of a developer who was absolutely CLUELESS about how subversion works and ended up undoing a bunch of my changes. ARGH!

I decided to rollback ALL her changes and let her reapply the commits. Here's how to do it:

svn merge -r [current revision]:[last good revision] .
 

for example

svn merge -r 90:88 .
svn commit -m "Undoing a clueless commit"