This is better than TrueCrypt-on-Dropbox [1] in the sense that there's probably much less bandwidth inflation due to encryption, if any.
However, with EncFS be warned:
"Anyone having access to the source directory is able to see how many files are in the encrypted filesystem, what permissions they have, their approximate size, and the last time they were accessed or modified." [2]
Since tarsnap does the block partitioning and encryption client-side, it doesn't suffer from either problem.