Looks like Inov-8 is making some adventure racing backpacks that look pretty interesting. The largest is 30 liters and weighs about 20 oz.
The interesting feature about these packs is the proprietary water bladder. They are using a 2L bladder that sits horizontally in the bottom of the pack and goes from one end of the hipbelt to the other end. Apparantly it can also be removed for refilling without having to get at the main pack.

