The Camelbak Flowmeter.
According to John the flowmeter fits inline with any Camelbak hydration hose and should cost $30. Finally, you will be able to monitor your fluid intake without taking the pack off and checking how full the bladder is.
My own observations: It's digital so it's going to need a battery. The added weight will probably cause the hose to move (sway) more than usual. Probably not a problem on the bike, but for running I'll need to figure out how to secure it. I wonder how the internals will deal with anything other than water, such as Gatorade, Powerade, etc. Hopefully it's water resistant and works in colder temps.
I perused the Camelbak website and couldn't find any signs of it, which is pretty typical with show stuff. I would suspect we could see it in stores later this year or early 2010. Any thoughts? Too much gadgetry for the trail? Is this something you've been dreaming of?