I'm currently administering about 8 server machines running Ubuntu. Right now, the 4 people with authority to ssh to the systems all share the same private key. This was fine when it was two people and two machines but it's not a good solution anymore. Should I setup an LDAP server? Any other suggestions?
Perhaps SME Server? Easy to set up and get going within 30mins or less (including LDAP setup). A short list of what SME Server offers can be found here. You could also look at Samba or 389 Directory Server for authentication.