One of the best things you can do is generate a key per device, not per person. That way if you lose your phone you just revoke that key and not the one that you use on your tablet, work laptop, home desktop, etc.
Bonus points: monkeysphere and certificate based auth are two other great solutions for making sure the ssh server you log into is not doing a MITM on initial connection (you know, the part where it asks you to manually verify the fingerprint of the server key and you likely just hit y instead).
Forwarding your ssh agent to a host that you don’t know for certain is not doing a MITM attack on you can be devastating, as is entering a password into same.
