As of 2013-11-23:
- Free = Less than 0.1 mBTC.
- Free transaction relay is capped at 15k/minute
- By default free transactions must have a priority of 1 BTC * 144 blocks / 250 bytes.
- 144 blocks is 1 day if the average block takes 10 minutes.
- Eligius will add a block which pays at least 40.96 uBTC per 512 bytes. 
- Transactions containing outputs of less than 54.30 uBTC are considered non-standard.