The Natural 4000 is a bit hit or miss. I've had 3; two were excellent, but one is merely acceptable. The action of the keys isn't as smooth, and the space bar initially required a slightly firmer press. The space bar seems to have loosened up over time, though, and I got used to the key feel quicker than I was expecting - but typos ARE much more frequent on that keyboard.

The inconsistency is a shame, because as a keyboard I really rate it. Good shape, comfy palm rests, standard layout, unintrusive media keys, and the stupid (but seemingly inevitable) F-Lock feature starts out disabled.

The action is not quite as nice as the previous Natural Pro model, but it's a lot quieter...