We love most everything about Timbuk2 bags except for the price tag—they're not cheap, to say the least. But REI has Timbuk2's Commute notebook messenger on clearance for $40, knocking 60 bucks off the retail price. The notebook pocket is 13.8 inches wide, if you're wondering about size. [REI]
I had one - It's a durable bag, but it always hurt my back no matter how much or how little I carried in it. I tried wearing it high, middle, and low to no avail.
I went back to a traditional backpack for school and tried other messenger-style bags for work. I haven't had back problems with any other messenger bag since then so I don't know what it is about the T2 that did that to me.
I got rid of it in my last move.