I just bought the Osprey Manta 30...I think you could easily fit a smaller (i.e. 13" Macbook or similar) into the larger pocket, still leaving room for your other items.  I wouldn't hesitate to use it as a daily pack for a school or work commute.

Tires...I've ridden and raced religiously on Schwalbe Racing Ralphs Snake Skin tubeless for the last 3 years.  This includes Leadville, Breckenridge and Gunnison and some of the CT.  My problems have been very few and far between.  IMHO...best tires ever!