There's been a few threads recently asking about bags etc so just thought I'd share the fact I really rate this bag (I've tried any combination of Deuter / Osprey / courier style bags etc). Been using mine for 18 months odd now and yet to find a better bag for on the bike. Expensive yes but very comfortable, has space and routing for a bladder, doesn't shift about on your back at all and you can fit a surprisingly large amount in / on it. With the aid of 3 bungee-cords I did just under 20 miles to work with this on my back this morning:

Change of clothes, lunch, book for the train, toolkit and random bits from my Cannondale Beast of the East.

Try doing that with a wingnut or Camelbak!