I play in any key the music is written in, or if I want to learn a song I simply download the MP3, listen to it and then I can play it back straight away in any key I want to.

When I used to go out with my band we already had our songs set out in the key set for the singers own range, but nowdays I mainly play for the odd sing a long nights which makes more money to be honest. The singers just walk up to you and give me their own music, so I don't want what key it is going to be in advance which makes it a good challenge and keeps you on your toes.
I sight read extremely well and can also tranpose in my head without having to use the keyboards own tranpose button, which quite frankly makes people lazy.

I've heard people and especially organists play in the same key all night. To my ears it gets to sound rather dull and repetitive after a while and the feeling/ambience can be lost on certain songs where they are simply meant to be played in their original set key, but if it gets you work playing in the key of C all night then good for you - go out, earn some money and pay off the bills, that's all what matters and if you and your crowd enjoy it as well, you must be doing something right