it mean's that it would be good, but its nothing you have to do. I found that 1and1.com are offering $0.99 yearly biz domains ($6.00 with some tax and additions here and there).
Seriously though, you don't need to have a domain to run the system, I am pretty sure that if you really wanted to, you could use a dynamic domain for it, but you'd have to chop at MyDNS's Expert configurations to get it working right.
If your not using it to send email to your friends down the way from you, it would not work unless your sharing a connection together. mail servers talk together and require an MX Record from a domain, most times thats not possible without registering a domain.
I really don't know how to be much more help with this, so I hope this helped