I've been using the plain, MS Natural keyboards for over a decade; all the way back to when they had normal arrow key & home-cluster layouts. I buy one for every computer I use with any regularity, which turns out to be one at home and one at the office.
My biggest complaint is they're not super durable. A single spill of water will destroy the keyboard (I've gone through about 5 this way), and the buttons do wear out over time (my home keyboard's '1' key is wearing out).
As you say, a better built, mechanical MS Natural would be God's Own Keyboard.
I am also using[1] microsoft natural keyboard, because it is the best (for me) combination of ergonomic split-hand slightly skewed keyborad that has normal querty layout. BUT.. the quality of the kyeboard is terrible. I with it the MS Natural would get Cherry MX Clear keys and better wireless tranciever.
If you are into straight keyboards, http://pckeyboard.com/page/PC122/UB40B5A