Solid long-term buy
I bought the Microsoft Natural Ergo Keyboard 4000 from Amazon in December, 2007 and I've had it at my desk since. The ergonomics are very well designed for my hands, the typing is quiet and the keys well cushioned. 3 1/2 years later and I'm only now considering replacing it, and that's based solely on some of the paint coming up and that I don't feel like giving it a good cleaning. I have never had a problem with the board itself or the software. The mechanics of the keyboard are still very solid. I have definitely gotten my money's worth and strongly suggest this to anybody looking for a new ergonomic keyboard.