
ssh -vvv -p 22 hostname.username.members.mac.com.
Where hostname is the name you gave to the machine (i.e. the name that appears in Finder), and username is your .Mac username (i.e. if your email address is steve@mac.com, your .Mac username is steve). Note that there is a "." at the very end of the command -- I've had more consistent success using it that way. You can also try Terminal.app » Shell » New Remote Connection (or press Command-Shift-K) and then look under 'Secure Shell (ssh) for "Discovered Servers"'.
As with all things Back To My Mac related, success is flakey and your best bet is if you have Airport Extreme base stations on both the local and remote machines.