What's the point? -- Have you seen the video of the two crazy scientist guys who did an experiment combining Diet Coke and Mentos to create a fountain that mimics Las Vegas' Bellagio fountain? This is those guys' - Fritz Grobe and Stephen Voltz - official site.
What to look for --You've probably seen the final experiment on YouTube or Google Video (though the site asks that people not post it there). Here, you can also see videos from other stages, including one that goes awry. More videos are to be posted soon.