I've been using a Macbook for a couple years now, and really love the thing - but it's had an annoying sleep disorder that I finally found a workaround for.
I rarely shut it off, usually just closing the lid when I'm not using it, so it goes to sleep. The problem has been waking up back up - often I'd open the lid and start to enter the password to unlock the system, and the screen would go black and the machine would act sort of half-asleep. It almost seemed like it was confused as to whether the lid was open or not - maybe it was something with the lid sensor (which some other discussions online hinted at).
It turns out there's a command-line utility to change some power settings, and using it to set the machine not to wake up when the lid opens seems to help. The command is:
sudo pmset -a lidwake 0
The machine still goes to sleep when the lid closes, but now after opening the lid it waits until I hit a key on the keyboard before it rouses itself. After 3 or 4 days of this, it hasn't acted up yet, so I think this is a good fix.