Anybody working with a computer probably spends a third to half of his time (when not a lot more) typing on a keyboard. Keyboards are mechanical devices (if yours isn’t, then please do change it now!)
Mechanical devices are not eternal, and the more you use them, the worse they function, unlike brains for instance, which aren’t eternal neither, but usually do work a lot better if you use them often.
A good keyword costs less than $100, a great one usually less than $150 ( no, I did not consider the $2000 Optimus Maximus ).
The feeling and comfort of typing on a brand new keyboard are so enjoyable, that nobody should use one older than 12 months. Ok, if you work on a laptop you can keep it two years, as you probably use it only half the time anyway… using a real keyboard when at home, right?
So, treat yourself, buy a new keyboard!