I was getting a bit annoyed trying to add some maps to my n95, it refused to let me go into "mass storage mode" as it was already being used by another application.
Holding down the applications button only showed standy as being active.
However..... I found this.
"However there is a workaround. If you launch ShoZu, then hold down the application button (the little dot-square-swoosh button to the left of the central button), you'll see a list of running applications. Find ShoZu in this list and press the 'C' button and agree to exit ShoZu. You should now be able to use the USB mass storage"
So you have to start Shozu, and close it in this way not just exit or it lock the memory. A bit of a pain, but now I know its not so bad a work around