Recently I’ve been having problems with Ubuntu and sleeping my laptop and it turns out it has the strangest cause. I even rolled back to a 9.10 version since that used to work. And it did for a while. Then it stopped. All I got was the sleep light flashing constantly.
It looks like the issue was actually having an SD card in the reader on my laptop. As soon as I took it out I could sleep as usual.
Thanks to this thread for the suggestion – http://ubuntuforums.org/showthread.php?t=1470067