I've been a daypack carrier for years. Rain or shine, around town or travelling, my backpack was almost always with me. Until now. Like most people, I couldn't help but notice that messenger bags seem to be taking over the world...so I decided to take the plunge and picked up a Small Classic Messenger recently.

Things I Like
*Timbuk2 seems to have very good workmanship. Plus the lifetime guarantee matches what most major backpack makers offer.
*The bag really stays put on my back. Unlike a lot of shoulder bags, once the messenger bag is strapped on and hitched up, it hardly moves around at all and is very stable.
*On crowded public transit, a messenger bag doesn't mow people down like a backpack.
*There's a key fob and lots of pockets.
*It's possible to access the interior of the bag without taking it off.

Things I Don't Like
*When the cam buckle is latched in the "bag up" position, there's a big loop of strap hanging loose. It's easy to get caught on things if you're not careful.
*One shoulder takes all the weight. When the bag is really loaded down, it gets uncomfortable.
*For some reason, the bag looks bigger than it carries. When I first got the bag, the inside seemed gigantic and I didn't think I would ever fill it up. In practice, however, the interior is rather narrow and is really not as cavernous as I thought it was.

Bottom line: none of the things I don't like about the bag are showstoppers. All in all, the Timbuk2 Classic Messenger is a well-made and functional bag. Now, when I don't have a lot of stuff to carry or I don't want to be weighed down by a full-blown daypack, I use my messenger bag. Four stars.

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Addendum
Many reviews here mention how noisy the Velcro is. Timbuk2 offers Silencer Velcro Strips on its website in the Accessories section. I use them whenever I bring my bag to a place where Velcro ripping noises would be disruptive. Also, when you get a new bag, you have to look in one of the interior pockets to find the removable cross strap (except with XS bags which don't include it).

Addendum 2 (April 2014)
Timbuk2 really does take its lifetime warranty seriously. I recently sent them a bag with fabric and stitching that was beginning to tear. They are repairing my bag and returning it to me at no charge, even though I've been using the bag for over a year. Nice!