In reply to ajsaddacs: Over the last few months I've done a lot of running and cycling to/from work (approx 5mile at a time) with an Alpkit Gourdon 20, and was pleasantly surprised at how well it performs.
I'd bought it wanting a dry bag in case I was commuting in a deluge and not expecting much, but was surprised to find it one of the most comfortable rucsacs I've used, especially for running - it seems to sit a lot more stable than most I've tried.
The only issues I've found are that having just a single compartment, things like keys have a habit of migrating to the bottom and so can be an arse to find at times, and if fairly empty I struggle to get the compression straps to close in quite tight enough and I can feel some things moving inside. That's not really an issue if there are enough clothes in to damp out the motion though.