It is by far the most-viewed video in the history of The Inquirer/Daily News website philly.com, with more than 1.2 million visits to the video's page in four weeks.
A YouTube spokeswoman says that the way the video has spread is classic viral - quickly and exponentially - but that it is "remarkable" for cultural material to do so.
In terms of competition, "Nothing springs to mind in terms of something from the classical world," said YouTube's Annie Baxter.
As a calling card for the city and its culture, the Opera Company's stunt might be the digital age's answer to the Philadelphia Museum of Art's 1996 Cézanne blockbuster show, which drew 548,741 viewers. But those consumers of culture were flesh and blood, spending money in the city. Are there tangible benefits to this new breed of virtual cultural tourist?
"What the opera did could stick like Cézanne - if we made it stick," says Meryl Levitz, president of the Greater Philadelphia Tourism Marketing Corp. (GPTMC). "It won't happen by itself, just by virtue of the medium of the Web, which makes it increasingly easy to reach people and increasingly difficult to influence them. Marketing is needed."
Opera Company executive director David B. Devan is working on it.
"One of the things I have on my agenda is to ramp up that discussion with the city, GPTMC, and other people who brand the city," he said. "Is there a way that this kind of thing can be developed for [hotel] room nights, for restaurants? Is there a way for this to equal local economic impact?"
For the Opera Company, the episode has been measurably beneficent.
No bump in ticket sales has been detected, but Philadelphia's little opera troupe - with a $9 million annual budget that's a quarter of those of the city's largest arts groups - has received about $1,000 in small gifts as a result of the video, and is on the receiving end of a generally nice vibe.
"This kind of success is igniting philanthropy," Devan said. "Every major gift call I go on, the first thing out of everyone's mouths is how great our YouTube stuff is."
The funding for the venture was itself a gift: $30,000 from the Knight Foundation, which awarded the money after the Opera Company staged a similar April ambush with Verdi at the Reading Terminal Market.
With these electronic media forays under its belt, the Opera Company feels confident in developing steps to take its Puccini, Mozart, and Bizet beyond the 153-year-old, 2,900-seat Academy of Music it calls home.
One idea being explored is moving an opera production out of the Academy and into a movie studio for specially adapted versions to be distributed online.
"The Met has had a good run of HD broadcasts, right? So OK, live simulcast, someone else has that covered. But maybe some of our learning from YouTube with purpose-filmed, purpose-produced stuff - we have some proprietary knowledge about that now," said Devan.
But an audience in the millions for pure opera seems unlikely. The Opera Company's Messiah video hit several distinct constituencies at once: wags and joy-mongers, classical and opera lovers, Christmas nostalgists, and Christians savoring a sacred event in a secular setting. It certainly helped that the video was launched as the Christmas season was gearing up.
It's been linked on blogs and websites worldwide - far beyond the usual classical music chattering class, to inyourfaceradio.net, readingkidsbooks.blogspot.com, reformationanglicanism.blogspot.com, and hundreds of others.
Devan isn't alone in pointing out that the number of people claiming to have actually been at Macy's that day is growing, coloring the event in shades of Woodstock.
It made online commenter bkwyrm "hopeful and happy to the point of tears."
1947invictus saw it as "bringing classical music to the main stream of society!!!!"
"This is probably the greatest video ever shown on YouTube," declared theredarrow78.
Wrote sdoublait: "All I see in this video is a bunch of overweight, poorly dressed Americans out buying things they do not need and cannot afford."
Ah, well, everyone's a critic.
Authors of the American Culture website took the Macy's sing-in as a validation of Christianity in America.
"Once in awhile something special happens in American culture to bring joy to our country's vast population of Christians, and especially those who take their Christian faith very seriously. We are more used to being the butt [of] jokes and ridicule, or the object of libertarian fears, and more often than not just ignored."
Noting the millions of views, the author adds: "Take that, you mighty secular elites!"
If intent matters, nothing of the sort - no religious messaging - was considered when the Opera Company chose Handel's piece for the sing-in.
Requirements were a work that hundreds of choristers would already know, and one that would make use of the Wanamaker Organ.
"That's part of the adventure when you go to a wide platform - everyone is going to take something different from it," Devan said. "These viral things have a life of their own."
To view the Macy's flash opera online, visit
Contact music critic Peter Dobrin at 215-854-5611 or email@example.com. Read his blog at www.philly.com/philly/blogs/arts