Comment 14 for bug 903422

Once again, just to put the story straight: Android 4/ICS is ***still*** supporting USB mass storage (UMS). The only thing is that some devices (such as Galaxy Nexus) have only one partition (i.e. without SD card) and thus, can't rely on UMS since this would lockup the whole system. These devices have to rely on other widely known protocol like mtp and ptp which are usually supported under Linux for years. On this explanation, see:

So basically, the only thing to resolve here IMHO, is to have the Galaxy Nexus well recognized by Ubuntu as a mtp/ptp device (and, if possible, to provide complete file access with these protocols).