Thought I may have missed that screen on mine. So I just checked. Once I mounted on my Mac - there is NO unmount on the pulldown menu on the droid. So.... I'd say it does know when it's mounted to a Mac or a PC. No big deal, I'm just so used to cmd/e (command eject) I do it without thinking on my Mac.To unmount when connected to the PC, on your Droid, drag down your notification menu and tap on "unmount". Then it's safe to unplug from the PC.
When i mount my sd card to my PC running Win 7 a pop up box appears. it says Do you want to scan and fix removable disc? There might be a problem with some files on this device or disc....
Options are scan and fix (recommended)
continue without scanning.
If I select scan and fix it mounts the sd to the droid again. If i continue without scanning it works fine. anyone have this issue?
...You do not need to unmount it...It does that when un-pluged from the USB cable...
You do if you're using a mac. And why not unmount on the PC? Its what you're suppose to do.
mac - eject
everything else - don't worry about it, just pull the plug!
unless your talking about from the droid itself and not using your pc. in which case use sdrescan from the market. i use it when adding photos to my sdcard and wanting them to show up on the gallery without rebooting. (same goes for music)
edit: or when adding .nomedia to a directory on my sd card.