When starting my system I would expect that all external drives are automatically mounted while the internal drives are not mounted. This would be the behavior I am used to from Gnome 2 and as I know this is what should be expected from Xfce too. But in fact I get no drive at all mounted causing Rhythmbox not finding my music which is located on an external USB drive for instance.
This seems to be a duplicate of bug 3490. (I am not sure if bug 3490 includes that "internal drives [should not be] mounted".)
The "internal drives [should not be] mounted" part may be a duplicate of bug 7555.
Is this still valid? If yes, please reopen the bug, I'm closing it now.