Reposting from the bitcoin-development mailing list:
Mining support for BIP 16 is still under 50%, and won't possibly be over 50% by March 1. Which means we need a new evaluation/switchover date:
Re-evaluate support: March 15'th
Target switchover: April 1
If you're already supporting BIP16, restart bitcoind with the argument:
-paytoscripthashtime=1333238400
... to delay switchover until April 1.
Hopefully this will be the last delay; Tycho has told me that the deepbit pool will support BIP16 as soon as he's able to merge and test the changes, which will put support at well over 55%.
If you are a solo or p2pool miner you are strongly encouraged to upgrade bitcoind/Bitcoin-Qt in the next month; if you don't, you risk creating orphan blocks that the rest of the network will reject (and that risk will rapidly become greater over time as BIP16 transactions start to appear in the main block chain and get relayed across the network).