I've been commuting with a camelbak (without the water bladder) for over a year and I really like it. The key for using a backpack while commuting is to make it as small, light and comfortable as possible. I keep shoes and sweaters at work, so I usually just have some light clothing items, tools, lights, lunch, etc. in my camelbak. The pack is lighter on the way home because it is without the lunch and lights are on my bike/helmet.