I own a Lowepro Nova 4AW and as a carrying device its superb, strong, waterproof (with the all weather cover). But as a shoulder bag, it's incredibly uncomfortable to carry for long periods.
The bag is actually rather wide making it stick out and get in the way by banging in to people in crowded areas. Also it makes your shoulders really ache and become fatigued quickly. You find yourself constantly throwing it all around your body trying to get comfy.
As a consequence I'm buying a back pack and the Nova will be relegated to short journeys and infrequent use only.
Hope that helps