By default, the sound that plays when an account logs in is disabled on Ubuntu 12.04. To turn it on again, you need to add the command to startup-applications again. To do so, click on the cog-wheel icon on the top right corner of the screen and click on Startup Applications...
On the appearing window, click on Add. Enter a descriptive name for the entry and the following into the command line:
The term in quotation marks, desktop-login, is the name of the sound that is played - you can change that to anything you want (it has to be in the .ogg format and positioned in /usr/share/sounds/ubuntu/stereo).