There seem to be a few glitches, but the only real problem was that I had to remember to keep my attention on the traffic, rather than getting too interested in watching it count down to the next junction.
The mapping is very clear, the routes that it found seemed pretty sensible, and the directions are easy to follow.
It can search for addresses, but I just stuck a virtual pin in the map about six miles from home. Then I let it guide me there step by step, then reversed the process to come home again. Naturally, I also did the mandatory bit of stubbornly refusing to follow instructions, and forcing re-calculations.
It only took a few seconds to work out the route, though when I chose somewhere further away it took a lot longer, and sometimes seemed to lock up altogether.
Most of the time it describes each junction accurately, but it sometimes seems to imagine a roundabout where there isn't one (either on the ground or in the map). I thought it was failing to recognise the names of some minor roads, but on checking that's because they are not named in the map.
I could have made good use of this a few weeks ago when I was trying to find my way through Stanmore, and I'm sure it's going to prove useful in future. But what has really impressed me is how much things have moved on since I first came across all this stuff about 18 months ago. If you haven't tried this out, then I'd encourage you to experiment, and join me in thanking all those who are contributing tools and content.