Using Adobe AIR technology, the BBC has developed a version of the iPlayer that is compatible with OS X and Linux. The press release states that the player has entered beta as of today and a final release is scheduled for February 2009.
The beta testing of the Mac-compatible iPlayer is being conducted through the BBC iPlayer Labs. The application download itself can be found here.
The beta version of the BBC iPlayer Desktop requires OS 10.4 and above. The site does not indicate if the download is a universal binary. The BBC iPlayer is only available for UK citizens.
Thanks to all those who submitted the tip!