When did double-shot keytops disappear?

[e.stiebler]

Zane H. Healy wrote:
> One of these days I'd like to find a really high quality USB keyboard.  
> While I do like keys tops that stay intact, I'm more concerned with with 
> the keyboard not twisting easily, and keys that feel good when you push 
> on them.

I'm using few of the old IBM/Lexmark keyboards from 1984 with an USB/PS2 
converter for years. Nice and heavy, so they don't move much after each 
keystroke.