Apple Inc briefly edged past Exxon Mobil Corp to become the most valuable company in the United States. Looking ahead, Beakingviews columnist Robert Cyran asks: Could Apple be the first $1 trillion company?

Three initial public offerings were postponed on Tuesday, the latest casualties of volatile market conditions. Nearly half of the dozen IPOs planned this week have now been called off and Fortune.com’s Dan Primack says it “wouldn’t be surprising if none of them get out.” Primack added that Boston-based Carbonite is the best bet to stay the course: “A source familiar with the offering puts its chances of pricing this week at around 70 percent, so long as we don’t experience another major swoon.”

AOL reported a surprise second-quarter loss, citing weaker-than-expected advertising growth. The news sent shares of the company plummeting as much as 20 percent.

A lawmaker called for BlackBerry’s instant messaging service to be suspended after rioters used it to mobilize in London and other British cities. Wired.com’s New York bureau chief, John C. Abell, was quick to respond in a post on Reuters.com: “We need to start ignoring the smokescreen that is the entire subject of how tech is responsible for bad or undesired behavior. That is the stuff of Fahrenheit 451-esque oppressive regimes.”

The same riots had celebrities burning up the Twittersphere, as Justin Bieber, M.I.A., Piers Morgan and Kelly Osbourne were among those posting updates on the social network.