So I went to the Apple Store, Best Buy and an Office Max to have a look. I have to say, I was really unimpressed with the InCase Sleeve which was a front runner in my mind. It really seemed like it doesn't offer much protection, only scatch protection really. Don't get me wrong, I'm not planning on dropping my Macbook anytime soon, but I'm more worried about compression protection. If I'm travelling I want to be able to put it in a overhead or in a car with other gear and not worry too much about it.
Most of the messenger bags didn't impress me either (Swiss Gear, Targus, etc). The Apple Store really didn't have much, but they did have a Brenthaven Metro Lite, and I have to say it was the only thing I saw all day that I felt would offer any protection besides a couple hardshells I saw at Office Max. They didn't have the Brenthaven Edge, which is one I'd like to look at. If it's small enough it could double as a bag and a sleeve, but I have a feeling it isn't.
Thanks for the thoughts- I'm still on the fence about a sleeve or a bag. Ideally I'd do both, but I already dropped most my cash on buying my Macbook. And when it comes to one or the other I think I'm leaning bag right now.