I use a screen off app(Screen Off RT) and with one setting I can now close my screen with just a flip of the phone.
I also have a screen on app(Auto Screen On) but I've only managed to get the proximity sensor setting to work so it's no good for me when I'm out(phone in pocket)
There's a "g-sensor" setting but I have yet to figure out how to get it working.
I'd love a fully functional app that used motion for both on and off!
Edit: just tried the "g sensor" and it works!