Although the co-ordinates are displayed at the bottom of the screen, it might not be in the correct format and it cannot be copied. In order to get the co-ordinates in the correct format and to copy same to use on a website or document you can follow these steps.

On the Google Earth Menu go to "Tools" and then "Options".
On the Google Earth Option window, centre left you will see a heading "Show Lat/Long".
Tick the "Decimal Degrees" option (commonly used on Google maps) - For GPS Users the best option is the "Degrees, Minutes, Seconds option.
Select OK.
You should now be back at the Google Earth Screen
To copy the co-ordinates.
Right Click on the pin under Places. (Left hand Column)
Select Properties
The co-ordinates will be in the format selected in the Google Earth Options Window, and can now be copied.