To answer your question, there are several things one must consider beyond just disabling Ethernet.
Encrypt your hard drive. You could use FileVault2 but I'd opt for TrueCrypt. http://www.truecrypt.org/
Make sure your computer is set to sleep quickly or to log out during inactivity. This will limit the potential of a physical attack dumping your keys from live memory via Firewire.
Most important: Do not connect to any unknown networks. For example. do not, I repeat, do not connect to the hotel network!!! This is a main attack point for corporate espionage.
Set firmware password. This really just slows down an attack. If you are targeted, this will be easily bypassed if they have access to your machine.
As for IPV6, it is likely you can just keep it off. There are two main probable ways your data would be compromised, physical theft and open networks. True Crypt would solve your physical theft issues, especially if you create encryption within whole disk encryption or some other obfuscating techniques. As I said before, do not connect to any networks that aren't owned by your company, even with another computer or device. Lastly, in regards to physical security. I have often recommended disabling the Firewire port. There are several ways to achieve this, the easiest being in 10.5 & 10.6, just deleting the /System/Library/Extension/IOFireWireFamily.kext and replacing it with a dummy file. I haven't done this on Lion, although I'm sure it's a similar avenue. You can also do the same to USB depending on your goals.