I also have a Carradice Bike Bureau - I tend to destroy bags fairly quickly in daily use, but it took a friend of mine crashing my bike at reasonable speed to put a small hole (that hasn't spread) in the cotton duck of this bag. Scraping it along things like roads and walls does nothing other than make the material slightly softer to the touch.

However, the weak point of the bags is the shoulder strap - for one, as eibeinaka mentioned, it isn't that comfortable. Also the attachment points aren't great if you're using the strap for the majority of most days - mine started to come off a few months back, and now the bag is at Carradice for repairs. Luckily they have a lifetime warranty on defects in workmanship, as I don't have an industrial sewing machine!

Overall, very happy with the bag, well worth the £50-ish I spent for it.