I bought the large from eBags.com and received it today. When I first pulled it out of the box, I double-checked the tag to make sure they had sent me a Large and not a Medium. It looks deceivingly small! However, I am able to fit everything in my list into the bag without any trouble. It's a bit snug, but there's still room for a few odds and ends if I pack smart. I'm perfectly content - the storage is perfectly adequate, and it doesn't even look overwhelmingly big.
I loaded it up and took it for a spin tonight - I have had a Chrome Metropolis in the past, and while it was superbly comfortable and very rugged, it didn't allow for the minutiae of adjustment the Timbuk2 permits. I like being able to manage the under-shoulder strap position, and I like being able to carry the bag comfortably at my side.
I'm definitely happy with the bag, and if it lasts till Christmas I'll probably ask for a second one from the girlfriend (bigger or smaller, haven't decided yet).
Now if someone could explain how to tighten the main strap under load with that crazy clamp device, I'd be a happy camper...