I've been using a Kinesis (Ergo Elan) for 9 years now. After about 5 years some of the little rubber keys started malfunctioning. Now my ESC and F5 keys no longer work at all and most other rubber keys only intermittently. I probably should open it up and apply graphite rubber to the keys to restore their ability to make contact.

I don't mind the size of the rubber keys, but I wish they'd make a keyboard with decent switches for them!