Amazingly when this was first released, Amazon listed the price at about £365. I wasn't intending to buy this lens until next year, but I could not refuse the price. The price shot up to £550 while waiting for the pre-order (1 month), but Amazon still honoured the price - Thanks!!
The price has now fallen in line with the more competitive suppliers out there, so go on you Amazon.
Anyway, the lens. It's perfect. Nice size and weight, well built, and the IS on this lens is a monster, really, really good. Sharp at pretty much every focal length and aperture, edge to edge. At 300mm f4 the furthest edges can be a little soft, but really not a distraction.
You won't find a lens this compact, at this price, that gives you an effective focal length of 200-600mm, with IS, and the quality that it does. Bravo!