Something quite puzzling happened to me... I just got a galaxy nexus and was disappointed to see my linux mint box fail to mount the phone automatically. I then read about the abandonment of UMS so I resorted to follow guidelines such as http://blog.mpshouse.com/?p=609 and that essentially involve using mtpfs. After much trouble getting it to work, I could finally copy files to my phone (though it was buggy).
Next day I plug my phone to my other linux mint box (laptop), expecting to go through the same process. Except it mounted it ok, just like any other USB storage. same version of mint (Linux Mint 13 Maya as per cat /etc/issue). puzzled..!
Any idea how that's possible? mtpfs isn't even installed on that other laptop... very confusing!