I just got one of these from my brother in law because the enter key (on the keypad, not the main one) is broken. Nice thing is, all the keys are the same size, just like my model M (which I broke). I rearranged all the letters and am waiting to use it. Just figured I'd let you all know that there is an alternative to the model M with respect to intechangeable keys.
Good stuff. Another good one is the Trust Silverline Direct Access keyboard I used to use... Some of the keys required a little surgery underneath - there's a groove to help the key travel cleanly - on the index finger home keys this groove is positioned differently. 10 minutes with a reasonably sharp pen-knife... Keep in mind you'll have to operate on four keys. This does void your warranty ;)
I also did some work on the keyboard of a Dell laptop lately. You can read about it here
apple pro keyboard