So far, and it seems numbers are rising. And that's just reported cases.

"there has also been a marked spike in reported incidents to NHTSA. Starting in 2013, consumer complaints to NHTSA more than doubled from the year before, from 41 to 100, and then nearly doubled again to 187 in 2014."
"What’s clear is that the consumer complaints in NHTSA’s database are only a fraction of the actual sunroof explosions occurring in the U.S."

I think that's too much, considering the sunroof ends up in your face. Some cars now come with "panoramic" sunroofs that cover most of the roof.

"An exploding sunroof might sound like a freak occurrence, but a Consumer Reports investigation has found that it’s not. These incidents have happened in every month of the year in every part of the country, in vehicles from all over the world; they have occurred on interstates, on country roads, and even while parked in driveways.

Sunroofs have significantly expanded in size in recent years, and they’ve also grown in popularity. And the number of consumer complaints about them shattering without warning has soared."

"Our investigation has found that, with a few exceptions, automakers are not acknowledging or resolving the issue. It’s also clear that the safety standards and regulatory oversight of sunroofs have not kept pace with those dramatic size and design changes and that more needs to be done to guarantee they are safe."

They do seem to break spontaneously as a result of quality control issues.

"Consumer Reports has read through those reports, and while some details vary, they’re identical to Heather Savage’s experience in this way: A sunroof suddenly shatters with no direct or known cause."

"The most common manufacturing issues, though, is contaminated glass.The presence of nickel sulfide, for example, can put additional stress on a sunroof when the crystal expands at higher temperatures"
"Automakers generally use the thinnest glass they can—about half a centimeter thick."

Some auto makers are taking action.

"NHTSA can investigate and order recalls... the agency has conducted four previous sunroof-defect investigations since 2004. Two resulted in automaker recalls"

"Audi and Volkswagen have issued sunroof recalls without NHTSA first opening an investigation, Audi for its 2012 Q5 and the 2013 - 2014 A8 and S8, and Volkswagen for its 2013 - 2015 Beetle."

Why not laminate it?

"But there’s no reason sunroofs can’t be big, spectacular—and safe. Auto-glass experts and structural engineers CR spoke with say there are ways to make sunroofs safer, beginning with the kind of glass they’re made of. Tempered glass, experts say, is sufficient when sunroofs are small and flat but not for those that are large and curved."

"NHTSA told CR that the agency is researching “the structural integrity of sunroofs in a variety of circumstances, including reducing passenger ejection.

"Some automakers like Volvo and Tesla have begun using only laminated glass in their sunroofs. Other manufacturers, including Ford, Honda, Nissan, and Subaru, are using laminated sunroof glass in some models. Drivers should ask the dealer before purchasing a vehicle"