I used to use the equivalent to an IBM model M from Unicomp (
http://pckeyboard.com). They're basically the people who split off from IBM when IBM discontinued that particular style of keyboard. Same employees, same keyboards, same factory machines. Same everything.
It was "fun" for about 2 years to have a keyboard that sounded like miniature grenades detonating under the keys every time you pressed something and the spring collapsed with a loud "CLACK". After a while, I found my fingers and knuckles felt like they were starting to wear out and I couldn't sustain any level of productive typing for more then a few hours.
I eventually switched to Apple's "pro" USB keyboards (the full sized, full key units- back then they came in white and black, then just white, then white without the numpad), and later the chiclet units as soon as they became available.
Frankly, the reduced key press on the chiclet keyboards has convinced me to never look back. They are extremely easy keyboards to type on, and I can type on them all day long without any kind of issues. In fact, I find it extremely annoying to try and type on a "normal" keyboard these days- the key press travel is just too long.
-SC