Well I did it - bought a Giant Twist Esprit Power for £1100, this is listed at £1600 so I think it was a fair price. The bike itself is built like a tank and has hub gears which suit me more than derailleurs (I already have an Alfine bike; this one has Nexus 7).
Electrically this has a 36V 10Ah battery, front hub motor and torque-sensor in the cranks - no 'throttle'. The motor gives assistance up to about 15mph then tapers off, going into freewheel at about 16.5 mph (I know when that happens, it's quite noisy!). Any cycling with the motor freewheeling is therefore unassisted.
I commuted in this morning, 10 miles down Blackpool sea front in a gale, and it's been a revelation. I wouldn't have cycled at all today without this bike.
The first thing is that it does NOT take the effort out of cycling; maintaining 15mph in a headwind is still quite hard work, but without assistance I'd have been spinning away at 9 or 10mph and feeling miserable. Out of the wind I find I'm tickling the motor cut-out, and with a tailwind I was riding 18-19mph, so not that different from a normal bike.
At the end of this trip the display was still showing all five bars of battery; that's not surprising given that I was putting quite a lot of work in myself.
The intention is to switch to my unassisted bike when the weather's OK but we'll see whether I've got the self-discipline to do that!
My main criticism of this bike is the torque-sensing system in the crank; essentially it's a spring which is compressed with each pedal stroke. This means that the pedals feel mushy if you press hard, which is particularly emphasised if you try to ride unassisted. In practice it's not a huge problem if you keep a high cadence and avoid stamping on the pedals, which is how I prefer to ride, but I could see many riders not liking it. I understand there are alternatives such as a sensor in the rear drop out, which I expect would reduce or remove this issue. (I've been riding with an Alfine hub for a couple of years now so I'm used to the sometimes indirect feel these can give; what I'm talking about is much more than that).
I use a bike for transport and a ride out in the local countryside at weekends; I don't ride long distance (30 miles is about it for me) and I'm not sporty; I'm also 49 this year. For people like me this kind of bike has a place in the future. I'll never want to lose the simplicity of a standard bicycle though, and at £1100 I won't be using this one to go to the shops!
[EDIT: as an aside, my previous second bike, a Revolution Country Traveller, is going to my son for him to commute to his work experience. He's learning to drive but has realised he can't actually afford to run a car and, more to the point, doesn't need one. I think he's got potential to stick with cycling]