The article contains a mistake - where it says "Don’t Copy Your Public Key Around" it really means "Don’t Copy Your Private Key Around".
The advice to use ForwardAgent is also dubious, at least without fully describing the implications - which is that if you log into a compromised host, that host can use your credentials to access other hosts.
Agreed, I personally counter this by having different private keys for different networks and levels of security clearance. My work key gets me onto the work networks, once inside, I have a network specific key to use inside the network itself. This way I don't need to use ForwardAgent and my personal boxes will not be compromised if my work or any of my friends are.
The advice to use ForwardAgent is also dubious, at least without fully describing the implications - which is that if you log into a compromised host, that host can use your credentials to access other hosts.