I've been using TortoiseSVN with Subversion for a while now. Its pretty easy to use and most of the time I just use the Update and Commit functions....and occasionally if I need to track down the author of a particular line of code I use Blame or Show Log.
Recently though, I made the mistake of directly copying folders and files from a different branch into the one I was working in...and on checking it in found that it broke things because it checked it in as coming from the branch I had copied them from. At that point I found out that what needs to be done is to use the commands made available by TortoiseSVN to copy and export the folders across so their references remain correct.
So it's left me wondering....What other power commands exist that are important for a developer using Subversion to know that help you from breaking things or reduce the amount of effort of performing various version control tasks?