i cant put my rig on sleep because for some reason it starts up again without me touching it :S
I had the Sam problem. I fixed by disabling the video card from being able to wake up the PC. Seems to have been just the trick.
sometimes, you may also have an option that "wakes from network activity" enabled. some options can be disabled from BIOS.
I almost always use sleep. It's faster then having to boot up each time I want to turn on my computer. I usually shut it down when doing an update or if I'm not going to use it for more than a day (doesn't happen often).
I usually sleep mine if I know I will use it again within 24 hours. If I won't be touching for a few days I shut it down.