I managed to shoot myself in the foot this morning by doing the following:
There is a solution... go to your recycle bin you'll find there the latest version of the deleted file. Tortoise "throwing" to the recycle bin every file that it revert.
You can't recover the files, if you are using svn command-line client.
But you can recover them, if you are using TortoiseSVN as your svn client. TortoiseSVN will automatically move them to your Recycle Bin. You can restore them from there after an accidental revert.
This is a configurable option in TortoiseSVN. It is under Settings -> Dialog 1 -> Use recycle bin when reverting.
By default it is checked, which means files are moved to recycle bin. If you want(mostly you don't care to disable this. If you have a reason, please let me also know)
No, SVN does not keep a log or backup (although there is a solution for TortoiseSVN noted in the other answers).
But in case someone is browsing the answers and did not notice this comment in the OP's question:
"Fortunately in this case I had done an "svn diff > temp.txt" before leaving work on Friday, and the temp.txt file was still on my hard drive, so I was able to feed that file into "patch" and recover my lost changes."
I imagine it is a common paradigm to do 'svn diff' BEFORE you do an 'svn revert'. If you get in the habit of doing this, even if the diff is just echoed to the terminal, you've at least got one possible avenue to recover your lost changes.
If you are using InteliJ then you are a lucky person. On the top menu, you have a Version Control option, and under it you will find local history option, where you will find all the history for selected file, including all the operation you did with that file (update,commit, revert ).
Good luck, Arkde