I've installed Ubuntu 12.04 on my Macbook (white). Whenever the OS goes into Suspend after being idle for some time, it does not resume upon hitting a key or moving the mouse. I have to bring down the screen and open it again, to bring it out of suspend mode.
Furthermore, getting out of suspend mode isn't always guaranteed to use the above method. Sometimes, the screen will stay blank in spite of closing and opening the screen multiple times. If this happens, I go to
tty2 (Ctrl+Alt+F2), and do a
sudo pkill -15 Xorg. This gets rid of the blank screen but kills all my open applications.