I recently decided to update my stable Raspbian Wheezy image because of the most recent incremental release. I had originally started with the October 2012 image and had updated/upgraded once before when the December 2012 release came out. Couldn't remember all of the different commands so I looked them up once again. It took a few tries because not all of the commands wanted to work nice together. The "sudo apt-get update" always finished properly, but when I followed that with "sudo apt-get upgrade", it finished with several errors and wouldn't reboot. Tried it more than once with similar results. What did work was to follow the update with the "sudo apt-get dist-upgrade". I did follow one suggestion to string the two commands together like this:
sudo apt-get update&&sudo apt-get dist-upgrade
I'm not sure if this is the normal expectation or if "apt-get" was just having a bad hair day.