Something like the built in "Ad Location" templates in vB?
I disagree, because as I'm sure you know, it makes upgrading templates a hassle. At least that was the case with vBulletin.I personally dont see the need. If you are going to open up a template to stick an advert in, it may as well be the actual template - would save an advert template being included into a main template, and reduce load.
(note: I'm basing this on an assumption of a similar storage/handling system as vb)