I think we all do from time to time. Fortunately, I know a guru who has written on precisely this topic. It's an article called Motivation & Uncertainty. His other stuff is also excellent.
I've decided to spend June learning Czech. Unfortunately, the course I wanted to attend is fully booked, so I'm going to try plan B and learn at home. I'll keep up with posts at the Ghost Cabinet, but my focus has to move away from this site if I'm going to make headway with Czech. Anyway, it will be an interesting experiment to track what happens to site traffic, when a blogger takes a break. I'll come back when Blair goes.