They're what I'm comfortable with and that makes them good.
PS: I didn't down arrow you. What's with all the Redditesque down voting lately?
Blub :)
Seriously though, I was a big Model M fan for a while. Then I tried something newer, and could never go back.
Also, the new keyboards are less likely to cause your desk to collapse ;)
That being said, the ergonomics of using a laptop-style keyboard is usually much better when it is external than when it is connected to a computer. The thinness of the Air might change this though, haven't tried it yet.
Which model, specifically?
I have a coworker whose right pinky finger starts hurting about an hour into using a keyboard. He replaced his no-name rubber dome keyboard with a Cherry Brown-based Filco, and the problem was solved. The advantage a mechanical keyboard offers over the standard rubber-dome keyboard is that you don't have to press the key to the bottom of it's travel to make it register. This limits the force that your finger is required to transmit to something like 60g, instead of an infinite amount as you press the key against the immobile bottom of the keyboard. Less stress, less pain.
Anyway, if you do get a mechanical keyboard, just make sure to consciously avoid bottoming out for a while. If you pound on it, it will still hurt.
My desktop setup is a matias keyboard.
Well, I tried the 11.6" in the Apple Store today. The keyboard is awesome. It is a full sized keyboard. There is nothing 'laptop' about it. So it is exactly what you are used to if you have been using the recent wireless keyboard.