Wow! A whole 1.3 microseconds saved. And to think I didn't see any merit in it:)

On a slightly serious note, I think a novice perler might actually find the "values become keys and keys become values" slightly more obvious than the reverse method, which relies on a pretty good understanding of how hashes work in list contexts, on their first viewing, but once you understand that, the presence of the big clue, R-E-V-E-R-S-E does make it pretty clear:)