I prefer very inexpensive and small keyboards like for instance the Mitsumi budgetline. The pricerange allows me to have at least one backup keyboard without straining my economy. With a backup keyboard I can take one of them apart and clean it thoroughly without having to think too much about damaging it in the process. My keyboards get quite messy after a while and for what I've seen other peoples keyboards get messy too. The main difference seems to be that I care about it.
Or I could give a regular grey keyboard a much needed paintjob to make it look nice, while hooking up the extra keyboard in the meantime. If I was to have an expensive ergonomic keyboard as the primary keyboard I would only feel very awkward with going back to a regular one for backup. The size of the ergonomic keyboards is also too big for my taste. Take a regular keyboard, add a wristpad and then you have a solution that is pretty good for your hands. Sit straight, buy a good mousepad with support for your hand (I use Everglide Giganta) and may have done more good to your hands than using a super-ergo keyboard.
One last thing that I haven't tried yet, but am sure that I will. With one of these really cheap keyboards you can take it and smash it against a wall or throw it out the window after loosing a clan-match of Quake3. Although I would love to do the same with an MS Natural Keyboard I seriously doubt that I really could after spending that kind of money on one, or two, given my need for backup. ;-)