I've owned these scales for about 5 months now and I really wouldn't want to be without them. They look great, function well, were easy to set up (even on a Mac!) and the batteries last a shockingly long time. Yes they are expensive, but given the functionality they provide and the amount of use they have and will continue to get I think it is reasonable.
I've been on a weight loss programme since the week before I purchased these and they have been an invaluable tool for keeping me on track. I have lost just over 5 stones in 5 months, and whilst I do not credit the scales with any of that loss I do owe a great deal to the daily motivation boost provided by these scales. I weigh daily (which I don't think is recommended) and the scales are synced with my Withings account online (all wirelessly) but better still they update 2 cracking iPhone applications which I predominantly use to monitor my progress (Withings app and an app called 'Weightbot' that provides slightly different features and a great progress and predicted target pane).
The measurements are pretty accurate for weight (I get weighed weekly, independently of these scales, and they are always pretty spot on). As others have said the Fat measurement isn't quite so accurate, but as a guide the measurements are adequate. The average fat mass trend over a decent time period gives me confidence that my diet is good and that my weight losses are attributed to fat loss and not due to lean tissue wastage - which is an important monitoring tool.