Happy New Year everyone!
Yesterday Michael Smith visited ANU and gave a fun paper called 'Two Kinds of Consequentialism'. Afterwards the pub conversation turned to whether epistemic 'ought' implies 'can'. My hunch is that many different things may be expressed by epistemic uses of 'ought' in different contexts, and (more familiarly) the same kind of thing goes for 'can'. And it might be that for each epistemic 'ought' there's a corresponding 'can' which it implies. Nonetheless, I suspect that all or most (or at least most of the common) uses of the epistemic 'ought' express things which don't imply the things usually expressed by 'can'.
There's a recipe for creating counterexamples to 'ought' implies 'can' in the epistemic case which helps convince me of this. Take your favourite case of someone holding an irrational belief that she epistemically ought not to hold. (E.g. Carrie's believing at 5.40pm that aliens are invading the Earth despite there being absolutely no evidence to that effect.) Then make it so that the subject's holding that belief is beyond her control in your favourite sense. (E.g. Specify that Daniel has attached a brain-manipulating device to Carrie's head so that when he presses his remote control button at 5.40pm she will start believing that aliens are invading the Earth, despite having absolutely no evidence to that effect.) These will be cases where the subject epistemically ought to refrain from believing the proposition in question yet it's not the case that she can refrain from believing it.
It seems to be possible to follow this recipe for various different kinds of epistemic 'ought' (corresponding to various notions of epistemic irrationality) and various kinds of everyday 'can's (corresponding to various notions of control). It doesn't work for the weak 'can' of bare metaphysical possibility, of course, but 'ought'-implies-'can' isn't very interesting unless the 'can' is at least a bit stronger than that.