If there is one key on your keyboard that you can just about get away with not using, it's C.
Mum's laptop is gradually breaking down as it succumbs to old age and the latest fatality is C. I had an email from Mum today with words in it like sekond, kool, resieved, exsept and whitsh - all of which made perfect sense! I don't think that there are many letters in the alphabet that can be exchanged for another and still make sense.
However, if any of your passwords contain that very C then you are in trouble!!
Updated to add that baby brother has a very very good point - nearly every website ends with .Com - which makes losing the C key a pain in the bum!!