I prefer the thinkpad keyboards myself and use a mechanical keyboard on my desktop (one which I consider to have the best tactile feedback available: a Topre Realforce).
However, as a dvorak touch-typist I was curious to find out just how well different keyboards performed, so a while back I did a 1 minute random word test on each and got (approximately) the following results:
#1) Topre Realforce: ~110wpm random, ~140wpm non-random
#2) White macbook (island style): ~98wpm random , ~120wpm non-random
#3) Thinkpad T420: ~90wpm random, ~110wpm non-random
I used this site to do the comparisons: http://speedtest.10fastfingers.com/
Would be interested to see what other people get.