My brothers iPhone's back broke, so he ordered a new one. Then he discovered those strange new screws on his iPhone and called me.
We ordered the iPhone 4 Liberation Kit and waited a few (very few!) days before we got the kit!
It was done in under a minute, and the old screws weren't damaged at all! Not that we'll be using them...
Hold the screwdriver at a 90° angle, push down, and screw counter clockwise with confidence. Push the driver against the outwards motion of the screw to avoid slippage.