Why shackle this into a tweet-driven communication protocol (requiring 4+ tweets per transaction) at all?

I suggest making a service completely independent of twitter, let's call it haveacoin.com or something (actually that's a pretty good domain, someone register it).

1. You go on haveacoin.com and say "I want to give 1 btc to @shazow" (or internets or carrots or whatever you want to call it). You can give your name if you want (let's pretend you're @stonetz).
2. It gives you a unique address to send your 1 btc, you do so and carry on.
3. I get a tweet saying "@shazow You have a fan! @stonetz sent you a bitcoin, collect it here! http://haveacoin.com/1234"
4. I go to the URL, it asks me to authenticate ownership of the @shazow account (via oauth).
5. This logs me in and I can withdraw the balance associated with the @shazow account by sending it to my wallet.

Once that's out and live, you can move on to email or Facebook or SMS or as many authentication sources as you can implement (I'm assuming it's obvious what the verification processes are for email/facebook/sms).

Now we have a Twitter-independent service that spans multiple communication mediums and doesn't require any fancy polling or stream monitoring. Win!

- shazow