The consensus from Tuesday's IRC meeting is to replace OP_EVAL with "pay-to-script-hash" -- a simpler, safer-but-less-powerful alternative for creating bitcoin addresses for multisignature and future more-complex transactions.
So please read the BIP: https://en.bitcoin.it/wiki/BIP_0016
And the source: https://github.com/gavinandresen/bitcoin-git/tree/pay_to_script_hash
Important dates:
Feb 1 deadline to try to get 50+% of hashing power to express support.
Feb 15: "full validation" pay-to-script-hash switchover date (assuming success on Feb 1)