I'd like to see somebody work on a "shun ill-behaved peers" patch.
So if one of your peers sends you lots of garbage (blocks/transactions/addresses/whatever) you just disconnect from it and refuse to accept connections from it for a while.
The trick is thinking really hard about what is really 'garbage' and what might be honest, it-happens-every-so-often weird behavior due to block chain splits or other network events.
The goal would be to prevent a wide range of denial-of-service attacks.