The grass is always greener on the other side.
edit: so that my post isn't a useless comment:
1. Go into system settings==>display==>smart stay (make sure it is disabled)
2. Go into system settings==>motion==>motion activation (disable motion activation)
3. Try disabling widgets selectively to see if one of them is triggering this buggyness you speak of.
4. Review/audit your installed applications from the market. Some apps are setup automatically to prevent screen timeout, or perhaps even wake the phone up with a notification...... and it's possible the setting is in conflict with Samsungs software!
Personally, I have no issues with my phone so far. But in my experience so far, I noticed "smart stay" will detect stuff that ISN'T your face and keep the phone on. So if you hit a button that turns the phone on in your pocket, it could stay on because of smart stay's failure to work correctly. If you find that doing any of these things causes your screen turn on issues to go away or any other buggyness to go away...let us know! You will be benefitting the community by doing so. Just remember, a good smart phone needs a good smart person (and patient) to operate it and learn it. After using the GS3 for about a month now, you couldn't force me to use the RAZR.