If you haven't used Regular Expression, you haven't lived. It's as simple as that :-)
I used the following RegEx to rename a bunch of files in the nifty XYplorer (more on that in another post):
In the case of XYplorer, what that did was rename a bunch of files from "The Stupid File.rar" to "Stupid File, The.rar". Pretty neat...not like the good old days when you'd have to rename each file by hand.