I got an iPhone 4 from a relative but the screen was shattered into a million pieces (fortunately a screen protector was holding it together. If I could repair it we'd have a free phone (+ repair cost of course)!
The repair went really well. The Magnetic Project Mat was absolutely huge - I don't know how many screws I would have lost without it - and the iFixit guide was perfect.
I ran into a couple issues with the cheaper LCD+digitizer I bought. One of the screws didn't quite line up in the corner and the LCD cable connector didn't want to latch. I ended up putting a little piece of cardboard over the connector under the wifi antenna so that it would stay pressed down. Seems to work fine, we'll see how it holds up.