As has IP over ICMP echo requests, which I have actually found useful: http://code.gerade.org/hans/

Not if you actually use RFC 1149. You're operating at layer 1 and 2 when you rely on birds.

I'm waiting for the day when RFC 1149 is expanded to incorporate a layer 2 tunnelling protocol. I suspect this issue is not the initial encapsulation but how to extract the original frame without it getting mangled.

> It might even be faster than RFC 1149

Depends on definition of fast, the latency indeed could be better, but your bandwidth is only limited by the size of your USB stick, and most often would be much faster than current solutions.

Not all of them. Some of them hijack HTTP, so you resolve your destination address as usual, but when you actually attempt to connect, you're redirected. This seems to be becoming less common, though, unfortunately.