I'm afraid this is quite a common question, but searching several times through the questions did not prove useful, and I'm really eager of knowledge here :D
I understand that keeping SSH private key well secured (strong passphrase, backup ecc.) is crucial, but I'm wondering about how much having it stolen is dangerous. An eventual attacker, once got our private key, could log into every server which has our public key in authorized_keys, right? But besides that, are there other things that he could use the key for?