I recently discovered London's first Quietway. Some dude I was cycling behind suddenly turned left into Deptford, and being curious about whether he was taking a shortcut I didn't know about, I figured I'd follow him (for a block or two, if he kept heading in the right direction; it's not like I'm a stalker or anything).
There was soon a big "Quietway 1" sign, and then another, and another, and I ended up following him the whole way into London. At a non-threatening distance, of course.
I'd heard nothing about the Quietways, and it turns it they're rather new. QW1 - the one I followed - is the only one, with more (apparently) to follow. The idea is that the routes follow backstreets, parks, dedicated lanes and the like. QW1 works its way through some council estates in Deptford, before going through a park, then following an elevated path past the Millwall FC stadium, then more council estates and finally back roads towards Waterloo.
My verdict: cool, but with its own dangers. There's plenty of "wheeee" factor given the paths, sharp turns and bends, but some of those would be far less appealing in the rain, or icy mid-winter.
Also, while it's a great way to get into or out of London without battling with traffic, and is just the thing for a leisurely ride, the route ends up being a little more perilous at commuter speeds. Because the route is so quiet, and goes down residential back roads, with more than a few blind turns, not only are cyclists likely to become complacent as they whizz along, but pedestrians and children are more likely to step out in front of you. I've had a couple of near misses already.
That, and once closer to London, the route crosses main roads, which means a lot of long waits at traffic lights.
Having said that, I've found myself taking the route a good few times now, for the novelty if nothing else. Now, if only there were a Quietway that allowed me to bypass Bromley Hill.