Taking a look at the Michigan legislation, and then looking at what happens with communications: Sending e-mail through a router doesn't alter the addresses, either of the adressee, nor of the sender. So, that isn't what they're after.
I don't think a NAT changes anything as far as the ability of law enforcement people to track you down. Afterall, your ISP assigned IP is still visible to any tracking device.
I've scanned some of the legislation just now, and it's full of boiler plate all encompasing cell phone usage theft, all sorts of data theft. Pretty boring reading, but I think before we panic we need to find a summary of this sutff. Reading it is going to put me to sleep for sure.
The links to the available docs are here:
http://www.eff.org/IP/DMCA/states
Or you can read the Michigan law, put in effect March 31st Here. Just hit the printer friendly version and you can print out the whole thing to read at your leisure
http://www.michiganlegislature.org/m...0-219a-amended
Yawns-ville for sure.