The Invisible Shield by ZAGG looks pretty much like most of the clear screen shields you see on the market, until you start reading the application instructions. Firstly, you don't just "peel off the backing and stick it on" there is a sponge applicator to wipe down the covering before you apply it. This eliminates any air bubbles very effectively. Also key, is the (full body) shield covers the back and sides as well as the front screen AND button. It really is a full body shield.
I have applied one of these shields to an Apple iPod touch and my first attempt got fluff on a corner (because I hadn't read and followed the instructions) so this time around, I washed my hands and dabbed my fingers on the applicator sponge as instructed. There is a "how to video" on YouTube which helped.
Once the shield was on, I left the iPhone overnight (12 hours) and in the morning it was dry.
I can now take a philips screwdriver to the screen or a key to the back (my current party trick) and not a scratch. Plus (and this is my personal favourite) the iPhone fits in every holder, docking station and accessory available as it is, with the shield on.