I had an interesting thought: Would it be somewhat possible to increase download speed (and potentially upload speed) like a download accelerator does, but using a socks proxy that splits your traffic over 10 concurrent SSH tunnels? It wouldn't have to be too sophisticated due to the nature of how this would work; you could simply have a program split the packets(?) over each tunnel with a SOCKS proxy frontend. In theory, it should work nicely. Is there anything out there that does this?
A tunnel encapsulates IP traffic inside another IP packet, which incurs additional bytes of traffic to transmit and receive. As well, on either side of the tunnel, traffic will incur delays as it's wrapped and unwrapped. Oh, and since traffic through a tunnel has a smaller MTU, additional overhead is incurred here as well. So, I cannot think of a situation where this would provide an speed advantage.