There seems to be an sleeping issue with at least Intel based MacBooks.
MacBook / MacBook Pro Reliability:
The superb sleep behavior of PowerBooks and iBooks has long set them apart from ill-behaved PC laptops — nearly instant sleep and wake, with no confusing modes to choose between (do I need “Standby” or “Hibernate”?). But the new Intel-based laptops seem to be having some of the same troubles PCs have long known.
I have the issue and if you search web, there seems to be many others with same problem. The problem is usually that when you put your MacBook to sleep, after few seconds the screen goes blank and the hard drive shuts down but then immediately, the SuperDrive makes a noise and Mac wakes up again. I try to close all the programs and shut down the network storage and bluetooth waking up and put it to sleep again, but no luck. It always wakes up. If I leave it there, it tries to go to sleep again and again and again… Sometimes it goes to sleep, but usually not.
I usually use MacBook with external display. If I run it on batteries without external display, it succeeds to go to sleep more often, but only then.
Apple has an article: Mac OS X: Why your Mac might not sleep or stay in sleep mode. It didn’t help. Apple Support discussions have quite a many threads about the issue, but no answers. The issue is most annoying.
How to Put MacBook Pro to Sleep, Always? I sure would like to know the answer.