Is it harmless to use the same ssh private/public keypair from multiple computers?
Solution 1:
Your key identifies YOU, so it's semantically correct to use the same key everywhere. However, using the same key on 3 different computer increases the chance of the keys getting stolen.
Solution 2:
I typically create an ssh key for each machine I connect from. That key has a useful comment so that I can identify each one, such as "mike-phone" vs "mike-laptop". In this way, if I lose one of the devices, I can easily remove its public key from systems I connect to without affecting my connection from other machines I use.
From a sysadmin perspective, its much better to have multiple public/private key pairs when things go south, while its more of a pain up front.