Originally Posted by
corripio
A rack and panniers (or even strapping your bag to the rack) makes life a lot easier and a lot less sweaty than a backpack (especially on a hot summer day). Also, unless you get a good one really meant for biking, messenger bags have a tendency to slide from your back to your side, basically getting completely in the way of actually biking.
I sweat thinking about getting the mail. Seriously, they is no chance of me not arriving at work completely drenched. The need for shower is absolute. This is true in all weather. I arrive just as sweaty (although not as hot) during winter commutes as in summer.
Most LBS' sell versions of messenger bags like Timbuk2 starting at $55-ish. The second strap on these bags makes it impossible for the bag to slip and keeps it in a nice, well out of the way from everything position.