I'm currently using an Nokia N95 mobile phone. One thing that always bugged me was that when plugging it in to a Linux machine via USB to copy files, it would always complain when it was disconnected about the possibility that data may have been lost, even though the file system was unmounted. I have just put up with it however today I found a solution:
# eject /dev/sdb
I don't know why I didn't try that earlier.