One of my favorite features of TortoiseSVN is the ability to bring up the log, click on an old revision, and revert the changes from that revision.
If you've ever dealt with a situation where you're asked to make changes to something, then someone decides to go back after you've committed those changes, the above is a lifesaver.
The only beef I have is reverting the changes from a previous is revision is totally non-obvious from the command-line. Did you expect the svn revert command to accept a revision number? Nope.
In reality, TortoiseSVN isn't actually doing a revert all. It's doing an svn merge!
So if the file index.php is at revision 500 and you want to revert the changes from revision 499, you do this:
svn merge -r 500:499 index.php
That reverse-merges the changes from 499 and modifies the file in your working copy. Keep in mind, you still have to do an svn commit.
Of course, if you change you mind, you can always do an svn revert to undo the merge.