Although in a different domain, I recently went back to "school" for a couple of days to check that my skills were at least as good as the Bright Young Things who will be my professional colleagues from next year onwards (was a bit worried that a decade in Third World France had dulled my mind's analytical edge). The session was a reassuring success, but with the unexpected side-effect that I can't stop thinking how great it would be to take up full-time studying again.