This shows the power of viral marketing combined with a ubiquitous, instantaneous distribution system. This media power is available to everyone, and we have barely begun scratching the surface of what can be accomplished with it.
Of course, Shaiman's musical features Jack Black, John C. Reilly, Neil Patrick Harris and a whole lot of other popular stars. That certainly drives the huge appeal. But all of that star power (not to mention Shaiman's own brilliant material) was spread through the power of the medium. Without a digital media infrastructure, Shaiman would have had to make DVD copies and put them in a rack at Whole Foods Market (or some other establishment where his intended audience was likely to see it). In other words, he probably wouldn't have bothered to create it at all. But the ability to instantly make it available to the world is really what made it worth doing. The digital media infrastructure facilitated and perhaps even inspired the creativity.
Of course, it is the power of this medium, and the fact that it is literally in its infancy, that caused the WGA strike and may well lead to a SAG strike in the not too distant future. Everyone sees where the entertainment business is going and they don't want to be left out in the cold. Both sides probably have some valid points, but they might well kill the goose before it ever lays its first golden egg. After all, over a million people may have already viewed Prop 8 - The Musical, but it certainly hasn't generated enough revenue to begin to pay for the production (if everyone hadn't been working for a cause instead of for their normal paychecks).