I have been battling with a black screen for a little while now when i boot into osx, sometimes it'll wake after 20 mins, sometimes not at all, but I have found a way to wake it immediately and I just thought id share.
Connect a single RCA cable from the Green component output to your tv sets composite input (usually yellow)
Boot osx as normal and you should see a poor monochrome image on your tv.
Click the blue apple and select 'Sleep'
The machine and display will go to sleep
Now, disconnect your rca and connect your hdmi / dvi / whatever
Press a key on your keyboard to wake the system.
Your dvi should now wake and display perfectly.
I have a standard TV right next to my DVI monitor so this is no problem for me, but would be a pain for those of you without such a setup, but i thought i'd share anyway.
Now we just need analogue sound from the RCA's working
cheers,
malty