Just discovered an excellent post (and good design) from Carryology.  They compare backpacks and messenger bags to determine who needs which.  It’s slightyly humorous while making good arguments for each.  I agree with much of what they say, and while I own both, for day to day activities, I prefer the messenger for the simply pure reason that it’s more stylish.  But for backpacking, I’ve never found a use for one.  Maybe I’ll try it on my next trip to appear more local and not so touristy.