I just put my MBP5.3 on standby and everything is going well.
I had a problem after one of the updates, I don't remember if it was .2 .3 or .4 that had broken the sleep.
Instead of going to sleep it would reboot and I would get the following error message: (Sleep Wake Failure)
I then disabled "Power Nap", also known as darkwake. And everything is back to normal. (it's still disabled since then)
Disabling "PowerNap" is necessary with a Terminal command:
Open Terminal and and write (or copy/paste) and press [Enter]:
Code:
sudo pmset -a darkwakes 0
You will need to set the admin password
Let us know if Onyx has solved your problem.