ok so heres the deal i had the same problem with my computer. i installed lion and when it wouldn't stay awake from sleep i restarted my computer and ended up having to bring my 2011 macbook pro to the apple store because it wouldn't turn back on. they ended up replacing my motherboard. when i got home it worked fine until it went back to sleep for a while and then started doing the same thing, i was so frustrated. i went back did a little complaining and to their head tech guy to talk to me. he said that when the computer wakes up like that and goes to a black screen that it is trying to start the screen saver. mine was doing this because i had the screen saver set to come on after 20 mins of inactivity. i guess the new lion system assigns a screen saver to come on automatically even if you haven't set one up, this is why the screen goes black because it is trying to show the screen saver that you haven't even set up yet and doesn't really know what to do lol. so the tech guy set the screen saver to come on never and i haven't had problems with it since. i really hope this helps because i know how frustrating and inconvenient this is...