I had a Timbuk2 Commute bag, and after carrying my laptop in it for four years through torrential Miami spring downpours, I couldn't be happier with it. I sold it and got a large messenger bag from them, and it's treated me well so far. If you're looking for a sturdy bag with a lot of room inside that's waterproof- that's what you want.

The ONLY issue I've had is accidentally hitting the quick-adjusting strap thingie and having my bag drop while walking around. But while riding I've never had any issues whatsoever.