There's also the trivial (but often unhelpful) advice of "be closer to the server" -- the problem is one of round trip latencies since the internal design of tar (and thus tarsnap) works on the principle of "read a block; do something with it; repeat". This is what I feel to be the biggest technical pain point in tarsnap, and I know in theory how to fix it, but every time I've started focusing my energy on it other things have come up requiring more urgent attention. :-/
