Many of you are familiar with the rubber band/washer mod to reduce impact on bottom-out.
Geekhackers' attempts on Cherry key caps:
Washers:
http://geekhack.org/showwiki.php?title=Island:5450Dental rubber bands:
http://geekhack.org/showwiki.php?title=Island:8857Did you know that IBM once had it as a standard option? Not on Model Ms, but on Wheelwriters with Model M style keyboards.
I picked up a few broken Wheelwriter keyboards today from a local typewriter store to salvage some fun keys (will show in a later post when I have time). When I popped the caps off one of the boards I noticed something unusual. There are rubber o-rings under the keys, and the large keys all have stabilizers (very uncommon on Wheelwriters because they use Model M style round inserts).
O-rings:

Stabilizers:

The slot for the stabilizers are glued onto the standard Wheelwriter plate. I have 4 other plates in different shapes and sizes and none of them have these stabilizer slots.
According to Jim, the owner, the rubber o-rings and stabilizers come as an option on certain boards, and they are fairly rare.
The o-rings are kind of stiff. I'm not sure if it's because they are old or they were designed that way. One thing I'm sure is that they are not meant to reduce noise. When the machine is typing, it is so loud you can hardly even hear the buckling snap of the keys themselves.
Edit: corrected the terminology from washer to o-ring. Thanks Didjamatic.