Education and enterprise applications of Second Life have not succeeded on a wide scale, and using SL for architecture, while extremely promising, will probably take 10 years to gain any traction, if ever. However, Second Life machinima has already gained mass market adoption, and until SL's user base grows, it's probably the only real world application that will. Take the 2008 hit movie Role Models, for example, which incorporated Second Life machinima as a plot element. Most notably, it wasn't used to tell a story about SL, but to simulate a videogame that's a significant part of this scene:
With a worldwide gross of $92 million, about 12 million people have seen this scene with Second Life, and about as many will see it on DVD, cable and broadcast television, etc. Second Life machinima is also a featured element in this year's Hot Tub Time Machine (estimated theatrical viewers: 8 million), and HBO/Cinemax's Molotov Alva with 41 million potential viewers. (Second Life machinima made an appearance in the TV shows CSI: NYC and The Office, among other programs, though of course someone could argue these were only an artifact of Second Life's 2006-07 hype wave, never to be repeated.) If R U There, the Second Life-themed feature movie shown at Cannes this year, gets an international distributor, add 5-20 million more to that view count.
The reason Second Life machinima has succeeded where other real world applications have not?
Clearly, because installing and using Second Life is not required to enjoy SL machinima. Unlike Second Life itself, SL machinima is a perfect complement to the way most people use the Internet now, for quick bursts of information and entertainment, delivered at YouTube speed. (In this case, often, literally: Looking at total YouTube videos with Second Life machinima, we're conservatively talking more than 10 million total views.)
Beyond that, from the content creators' side, Second Life enjoys a number of advantages that other machinima platforms do not: ownership rights that allow for-profit machinima, an extremely diverse library of settings, props, effects, and other elements, and a community of independent developers that can create custom software that vastly improves the quality of machinima. Finally, machinima is such a diverse medium that it can be used to enhance other real world applications, such as education (such as film school), or corporate training (like this Level Playing field instructional video.)
The irony? Despite all these advantages, Linden Lab has done little to promote Second Life machinima as a real world application, certainly far far less than enterprise/education, which has not paid anywhere near the dividends that machinima has. Consequently, almost all of the very best SL machinima, such as Lainy Voom's "Stolen Child", attract only a few thousand views. Perhaps this speaks to the Lindens' focus on driving user acquisition and retention, which is all about getting people to install and run the software. In that zeal, they've maybe missed the fact that tens of millions who've never even touched Second Life have already enjoyed Second Life -- just after the interaction was simplified down to watch, click, and play.