Hmm.... you're only talking about a one-time per import calculation, correct?

And the concern is the time taken calculating the hash, presumably when doing large imports?

I wonder whether the hashing can be done at sync-time, and pipelined into the process, reducing the total hash cost to the number of hashes that need to be completed until we find a track that needs to be transferred. (At which point, we are transfer bandwidth limited, hashing can continue in the background)

For record though, I've just md5sum'd 47 mp3s in 30 seconds, on a Celeron 500, so I don't think it'd be that big an issue. ( gnu md5sum binary on linux )