If they're meant to be, somebody will cook up a few great instances and show why monads and other abstractions were insufficient. Until that happens I don't think they need to be in people's standard repertoire. Applicative functors seem to be much more handy.
I'd like to know more about comonads too, but the only interesting article I've seen about them I can recall was this one about using comonads to build a zipper for managing location in a site menu.