Schwinn is using Li-Po batteries on their electric-assist bikes and claiming 60 miles to a charge (4 hour recharge). They're also claiming that the drivetrain weighs in at 10lbs, I'm not sure if that includes the battery pack but they look damn small.
http://www.schwinnbike.com/products/...ory.php?id=110
I'd love one, but I think it'll be a while before I can justify 2+ Grand for a bicycle.