Mc343ll/a
I just purchased the latest part number to replace the first generation one that died on me a couple of weeks ago.
I wouldn't hold my breath on Apple having solved the issue with failures.
It would be great to see a tear down video and analysis from ifixit.com
But so far as I know, the change has to do with the antenna.
Also, there are some known issues with the guest network during setup.
Basically if you enable guest network during the normal new set up, the device can't been seen in Airport Utility. Now, you can still connect to the device as an access point, but you can't connect to configure it. Confusing I know.
Also, trivial point perhaps, but you need a new version of Airport Utility to set the unit up. So you need to use the install CD that comes with the device. It's a different version of Airport Utility, but labeled "5.5 (550.29)".
What Apple should do is have a secondary connection to the hard drive, such as firewire, so that you can access the data, in the event of a failure elsewhere in the system, e.g. power supply.
Good luck