Couple of semi-random thoughts:

RE: detecting double spends:  I agree that extending the protocol to make double-spend detection better is probably a bad idea.

That said, I could see extending the information reported by the listtransactions/gettransaction API calls to report detected double spends ( == transaction uses the same inputs as another transaction in the block chain or memory pool). IIRC, now the code just drops double spends, so if this was done the implementation would have to be careful about being vulnerable to a "fill memory with bogus transactions" attack.

RE: badly-behaved nodes:  I'd really like somebody to start experimenting with algorithms for detecting well-behaved and ill-behaved nodes-- maybe starting with a dns-seed implementation.  I suspect people are starting to experiment with various types of Sybil attacks, which might explain why network connectivity has been so bad.

(sent from the Sydney airport, before a very LOOONG flight back to Massachusetts)
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Gavin Andresen