I've written a series of tutorials on the topic of spatial / visual frequencies as a part of retouching work which I thought the membership here might enjoy. They remind me a lot of old conversations we had on similar topics for skin work here when I had more time to post.
While I'm well aware that it's poor internet etiquette to just post a link to one's self, I hope that you'll read a segment or two before condemning me - these are long entries, and would be a bit much to have in a thread which I'd rather focus on discussion of the matter.
In any case, I hope they help!
Visual Frequencies - a Primer
VF - Tools of the Trade
VF - The Mechanics
VF - Why, Sean, Why?!?
VF - Dirty Secrets, Dirty Tricks
Happy Labor Day!