I bought one.
There is no rotation lock (so awful for using it when you're laying down) and no way to increase the (very small) text size in Windows Phone 7.5.
Also, the camera of the 710 is poor and the fact there is no continuous auto-focus doesn't help at all.
Sure, it's £110 (you have to buy a £10 top-up) but it's still beaten by Orange's Monte Carlo (ZTE Skate) in my opinion (which is also £110).
I've used one for development, and I've found it to be a fantastic little device. It's extremely solidly built, and I found the screen quite impressive (I believe it's not a ClearBlack AMOLED like the 800 and 900 have), and the OS flies on it, making it a very very usable price. Compared to the experiences I've had with Android devices at similar price points (and at quite higher price points), it's a delight to use. Low-end Android devices are invariably garbage.
Also, it's £99.95 on most of the networks. £110 is only on some of them.