The Microsoft Natural Ergonomic Keyboard 4000 is by far the best keyboard I've been obsessed with (and I occupationally some wear). The attack is pleasantly quiet, but with very well defined pressure point, the design is great. Speaking of design: At first I was very skeptical about imitation leather ... But I must say, a more comfortable wrist rest, I can not imagine at the moment.
Even Microsoft has learned from his mistakes, and now the F-keys are again default to the normal F-functions, if desired, you can override Additional functions - which is a clear improvement is too early.
If you your hands and especially the Kapilartunnel what you want to do good, you buy the Microsoft Natural Ergonomic Keyboard 4000!