Is it confirmed that the power down hang problem is caused by the nvidia driver.
The reason I ask is because I also have issues with wlan on my PC.
If I turn on the router before booting ubuntu the network newer connects. I then have to "disable network" followed "enable network" before it works.
Sometimes it connects but does not seem to be configured correctly. I used to be able to run "sudo /sbin/dhclient" in previous ubuntu releases but in 12.04 this command just hangs.