For the last several weeks at least, my system has been having trouble waking up from sleep, and sometimes it is quite difficult to get it awake. This has been happening with 10.5.8 and 10.5.7. What sometimes happens is that the login screen appears. If I don't login right away, it disappears leaving a black screen and cursor only. And stays in that state, so there is nothing that can be done to get it going via mouse or keyboard. The workaround is to press the power button briefly, and put it back to full sleep, then press it again. I am thinking of powering it off each night, like we used to do with Windows back in the 90's due to its instability issues. Too bad!