Comment 1 for bug 29563

one can unmount the usbdrives (same way as ejecting cd/dvd)
go to Places->Computer (or nautilus menu: Go-> Computer)
right click on the usbdrive you want to unmount. at the bottom of the pop up menu select 'unmount Volume'

if you have the icons for your usbdrives on the desktop you can do the same thing there.
it works fine for me.

mathias