I've used the v1, the Elite, the Pro, the 4000, and now the Sculpt Ergonomic (this comment typed on the latter). In my opinion, each has been better than the last.

It is pretty hard for to work in the same room as anyone using anything prior to the 4000, due to the loud spacebar, and even the 4000's spacebar is pretty loud. I do slightly prefer the larger hump of the early keyboards.

The Sculpt Ergonomic is a departure from the large-bodied models of the past, but for those pining for the past, give the present/future a try :).

Microsoft's HID hardware has, in my experience, always been great. Thank you, everyone who has made these tools possible.