We may never know what actually happened. A Facebook spokesperson declined to comment, saying "the trip in question is a private one."
Meanwhile, the owner of the restaurant, Umberto Pavoncello, insisted that Mr. & Mrs. Facebook didn't tip. In an audio interview in English posted online this morning by the Cape Town radio show 2 Oceans Vibe, Umberto sympathetically chalked it up to the fact that the Zuck would be criticized by the media no matter what he did simply because he's rich: "If he leaves a little tip, oh, 'a billionaire only leaves a bit.' But if he leaves a lot of money for a tip, then 'oh he's a very rich man who doesn't give value to money.'"
Going investigative, Italian newspapers discovered that "Mr. & Mrs. FB" also didn't tip on Sunday when they had dinner at Pierluigi, a historic trattoria by Campo de' Fiori.
Regardless of what happened, the 28-year-old Californian wunderkind (who has incidentally been wearing a hoodie and track pants during his Roman Holiday) may not be the most obvious model for other American travelers to copy when it comes to etiquette.
So, when in Rome, what exactly do the Romans do, and — more importantly — what do they expect American visitors to do?
For the lowdown, we turned to Brian Dore, co-proprietor, along with Maria Gabriella Landers, of Concierge in Umbria, named one of Wendy Perrin's 12th Annual Top Travel Specialists. Says Dore: "When visiting Rome, or any of the most popular Italian cities for that matter, our advice is to leave a tip of ten percent for a proper sit-down meal."
But when his clients follow his advice and leave, say, ten euros on 100 euro bill, they often worry they're being "cheap." Dore's advice: "Don't feel guilty. This is the local expectation for American visitors. But do tip the ten percent."
Dore adds another fine point: Some restaurants state that service is included ("servizio incluso"), which means no additional tip is required. That, however, shouldn't be confused with the cover charge ("pane e coperto"), which is something all patrons, including locals, pay —usually totaling about two euros per person. In other words, the cover charge is required and separate from the tip.
Chiming in from Rome, longtime resident Erica Firpo, city editor for Luxe City Guide Rome, notes that, as at Nonna Betta, most Italian waiters hand customers a slip with the price of the meal, without leaving a line for a customer to write in a tip. So patrons paying by credit card need to have small change to make the tip separately, which is different than the custom in the United States.
Cultural anthropologists may wonder what it is that the locals themselves do. Katie Parla, a Rome-based food critic who has created the popular Rome for Foodies app, chimes in: "Romans generally leave a small gesture of a euro or two per diner as an additional service charge or ‘tip’ if they are satisfied with the service or if they have the change."
While not everyone agrees on the proper tip, all the experts we spoke to were of a single mind on one matter: The Zuckerbergs had good taste in restaurants. Pierluigi and Nonna Betta are both worth adding to your long lists of restaurants for your next visit to the Eternal City.
See Conde Nast Traveler's original story here.