Last October as part of the wacky maneuvering leading up to the passage of the $700 billion bailout bill, Congress folded into the final bill the Bicycle Commuter Act of Congressman Blumenauer. At last, for their low-impact wear on the roads and their congestion-relieving activities, bicyclists can be compensated in the same way transit users are. This pork is especially sweet! It's a great step towards fair recognition of the social goods of bicyling.
The IRS is apparently still working out the details about the way it will be implemented, so you may have to remind your HR staff about getting your reimbursement. There's information buried in the IRS Publication 15-B (2009) page.
[1/28 update: The San Francisco Bicycle Coalition has some additional information here. But it doesn't look yet like there's total clarity on how to implement it.]
What a great way to start the new year!