Speaking of the network...
... is there any really robust, generic, low-latency, open source p2p network "middleware" out there?
I think using protocol buffers as the serialization format is a good idea, but I don't think just switching to protocol buffers "buys" enough to be worth the effort (at least not now, when transaction volume is low).
I'd like to see some experimenting with running bitcoin on top of a different networking layer (and use protocol buffers, too). Is there a p2p network that is designed to be extremely highly reliable and difficult to infiltrate or attack with malicious nodes?