Not giving instructions on the page on how to verify the info was weak. Github people, if you're reading this, please update that page.
It's a shame that hasn't carried through to the key audit page but there is (now) a link on how to verify keys (http://help.github.com/verify-ssh-redirect)
Most users will not have many keys (probably just one), and will be alerted if they see more.
I bet a lot of people would have verified their keys with instructions but didn't bother without.
I'll be honest - I didn't understand what those MAC address-type fingerprints were, and I accepted each key. Their email made me trustful, saying that probably no account was affected. I do feel bad saying this in public, but it is what I did when there was not more information immediately available to me.
The Linux instructions were
ls ~/.ssh/*.pub | xargs -L 1 ssh-keygen -l -f