Back to My Mac is a feature of MobileMe that allows you to connect remotely to your Macs. Usually this is for screen-sharing or file-sharing through the Finder, but you can also connect via SSH.
In the Terminal app (found in /Applications/Utilities/), you can connect via Shell » New Remote Connection, then click the "Secure Shell (SSH)" item, then the computer you want to connect to under the "Server" column.
But what if that doesn't work? In that case, I have two suggestions for you: first, use SSH v2 and IPv6. Perhaps it's best to show you the command and then explain it:
ssh -2 -6 imac.luomat.members.mac.com -v
The "members.mac.com" is consistent for all users. "luomat" is my MobileMe username. "
