Yes I do a secondary fermentation for all of my beers. That is when the yeast are cleaning up the fermentation byproducts, e.g. diacetyl and acetaldahyde.
Do I let the yeast clean up in the primary fermenter or the secondary fermenter? It depends on the beer. Lagers get long secondaries in kegs. Big beers and dry hopped beers get moved to secondary.
One should go by taste and not the calendar when saying a beer is done.
So I guess technically, I'm doing "secondary fermentation" in my primary fermenter and keg. I have only been brewing since Oct 2011, so I haven't done any real big beers or lagering. My first I racked to a secondary because I thought it would make it better, but after reading several comments on the subject, I've eliminated racking to a secondary with my "basic" ales.
I'll be attempting my first Tripel soon, so I'll definitely be racking to a secondary fermenter for that one, unless otherwise advised.