How many use a combination of both?
Yep. Also use WBConfig to change system colors. Mostly for visibility/legibility on all the above. I frequently shift a skin color in WBConfig to go with a wallpaper, sometimes add a texture for the same reason.
Also to a fair amount of tweaking in SKS on the vertical taskbars. They're a little contrary, you kind of either need to set their width to look good with the skin (much easier, just drag it), or tweak the skin for the width you like to use (much more "work"). What can I say, I like them skinny.
All great features as far as I'm concerned.
Flexibility.