Tools, Parts, and Instructions - 3 Reasons I Love iFixit
My Aunt dropped her iPhone 3GS and cracked the front glass.
Overall - successful. Heating up the adhesive to remove the broken glass was one of the hardest parts. Getting one of the corners started took a lot of attempts and a lot of heat. 2nd hardest part = scraping the tiny bits of broken glass off the corner she'd dropped it on.
Be VERY careful with the screws. While backing one out, it dropped and bounced off the counter onto the floor, never to be seen again (and there were 3 of us looking).
Using a heat gun probably would've made my struggles getting the glass off 1,000% easier (that's an exact estimation).