I have 2 timbuk2 bags - the metro (I use as a purse) and the large size. I did use the large size for commuting to school for a while when I first purchased it. Quality wise, Timbuk2 really is nice. Their bags are well constructed and seem to hold up great (though they don't have as many options as they once did, which isn't so great)!

HOWEVER, I have not found any messenger bag to be comfortable with any amount of weight in it. They don't have padded backs, so you have to make sure to put something flat against your back to stop things from poking you... And they're hot. And they can make my back/arms ache from the extra weight there. They do stay in place, though.

Bottom line - if you don't mind carrying something on your back and aren't going to carry much weight, get a messenger bag. Otherwise, look seriously at racks and panniers. That's my *much* preferred option for personal comfort