At Kreg, our position has always been that glue is completely optional - which stands in stark contrast with other wood joinery techniques. However, we also suggest that if you want the strongest joint possible, adding glue is the way to go. The great news is that if you do use glue, there's no need for hours of clamp-ups since the screws act as mini internal clamps while the glue dries.
Inquiring minds want to know... when you're building your own projects with Kreg Joints:
I always use glue. dampen both pieces with a wet rag, apply glue to both pieces, even the glue with my finger, screw it together and wipe the excess off with wet rag.
Almost always for the whole piece and always for the carcass. The only exception (and depending on the project), I like to do pre-assembly/dryfit. Occassionaly, i'll put together the whole piece without glue to ensure i've got everthing the way i want it, then i knock it down and do it all over again with yellow woodglue.