I've been making slow but steady progress on my at-the-network-level testing tool. I don't put a lot of faith in standards documents-- it is too easy to misinterpret or ignore them. Good implementation-independent test suites seem like a better investment of time.
What's working: python-based code that serializes/deserializes messages in both bitcoin's binary format (to talk to the node being tested) and JSON (so it is easy for us humans to tweak/examine test data). Connecting and requesting all blocks.
Still todo: actually start writing test cases, figure out what other tools I need to write to create good test cases, and start systematically going through the "rules of bitcoin" and devising tests to make sure the rules are being followed-- starting with the super-important "get this wrong and you split the blockchain" rules.
I hope to recruit some of you to help out with all that... I'll be creating a github project with my progress so far very soon.