Glas.t definitely solves the problem that I have with all screen protectors.  I don't like the feel of the plastic, and they're more difficult to keep clean.  I've gone sans screen protector for a while now and have not had any problems with scratches.  The gorilla glass on the iPhone is pretty durable, but I try not to test it by putting it in my pocket with change or keys.  I think putting an extra layer of glass on the back of the iPhone is probably more practical since it's much more prone to cracking and getting nicked up.