I still have my keyboard from my 386, that I got in '91. I had a keyboard from the machine I got in '95 last for about 5 years (rubber dome). the machine I got in '99, rubber dome keyboard came with it, and I went through a keyboard a year, for about 3 years.
'03 swapped back to a Model M after years of not having one. The spring retainer for the spacebar broke in '09 (reason I initially joined). Got a second model M, and used that until it gave up the ghost. I just took it apart this week, and I see some stuff on the bottom on the steel plate in a manner that makes me wonder if someone spilled something on it without telling me. Still if it did, it looks like it dripped down into the middle with the membrane, and out a hole on the bottom (so much for Lexmark's drainage channels). That's part of why I want to go cherry, since I can replace a dead switch easier than I can tear apart and replace damaged internals on a model M (now if someone made a modular buckling spring switch, that'd be freaking awesome).