Multiple public SSH keys and multiple work computers.

How do you handle having multiple computers you work from, for example work laptop, private desktop, private laptop, using public key authentication.

I've started to consider the idea of having one private/public key for all three of my work systems. Does anyone else do this? Is it insecure in any way?

Edit: Seems to me that I either play it safe and keep my work and personal keys separate, or use one set of keys for all hosts like a true lazy BOFH.