I don't have much experience with the 12" powerbook, what makes you prefer the 12" keyboard over the others?
It's hard to describe, but I find the 12" PB keyboard to be a bit more "crisp" than the larger PB/MBP keyboards. In a lot of ways, it has the same feel as the earlier Wallstreet/PDQ KB, albeit with less travel. By contrast, although I like the AlBook/MBP keyboard it is a bit "soft." I have two 12" PBs and several parts, and find them all pretty similar.
My experience with the new MB keyboard is limited to a few minutes of playing with them in the store. The keys had a nice feel(the same sort of "crisp" feeling as the 12" PB) but the lack of travel REALLY bothered me. I found them bottoming out far too soon for my taste, although I would probably get used to it if I used it regularly.
BTW, I went in today and remapped keys on my October 1991 manufacture Model M. The "Alt" key now functions as the Apple Command key, the control key as the Alt/Option key, and the (never used)caps lock as the(seldom used) Control key. I realize that remapping the "Alt" key probably seems a bit backwards, but as I rarely look at the keyboard when typing it makes the most sense to me to have one of the most used modifier keys(the Apple/Command key) where I naturally want to reach for it.
I live close to the Unicomp factory and have dealt with them in person. Back in the spring, I picked up a Unicomp Model M(standard 101 key) at a flea market for $5. It was an "officially licensed" University of Kentucky Wildcats keyboard, and I was quite happy to use it at work during basketball season(I work at arch rival University of Louisville). The keyboard I bought came without a cord and was missing the special blue "Alt" keycap. The cable is a stock item(this was the plug-in version), and a quick email to the factory turned up a blue keycap. I walked into the factory with the KB in hand, where they installed both parts right in front of me and also were quite excited to see the UK keyboard. I was told that they still get regular requests for those.
I've been putting off ordering a Spacesaver M, but need to do so.
(full disclosure: this post was typed from my 2012 MBP with a chiclet keyboard)