If you insert a usb flash drive, Gnome in Ubuntu Karmic Koala will pop-up an icon at your desktop. This is a Mac-like default behaviour of Gnome desktop, but Karmic has more. If you right-click the drive icon, a pop-up menu that shows up will present you whether to 'Unmount' the device or 'Safely remove the drive'. These choices seems redundant, but I think it is a smart design. If you click 'Unmount', the drive icon where disappear from the desktop, but the drive icon will still be available through Nautilus. If you want to remount the drive, all you have to do is click the icon at Nautilus, the icon would then re-appear at your desktop.