After a drop, the front glass on my iPhone 4 shattered.
I used the ifixit guide for repair, which was solid. There were a couple of spots where I could have used a little bit more detail, but on the whole it was great.
I will say I was shocked when the device powered up properly. :-)
Definitely keep the screws separated and labeled. I used little glass bowls. There's no way I'd use a mat. They're too easy to lose and you'll never find them again.