When Wes Harper's high-definition cable service went on the fritz a few months ago, he hopped on Twitter and tried to reach Comcast's customer service reps.

At the time, it seemed the best course of action, given Comcast's sterling reputation on the social-media service.

But Comcast ignored him, pushing Harper, a 26-year-old digital-media strategist in Naples, Fla., to take extreme measures. He began a campaign of "flaming" Comcast with withering tweets.

Eventually, he got Comcast's attention, and the issue was resolved.

Leyl Master Black had quite a different experience. Instead of looking for a Dell rep after her PC's hard drive died, Black got the rep to come to her.

After Black griped on Twitter, a blogger friend put Black in touch with a Dell expert. Problem solved. "It was so quick," says Black, 39, of San Francisco.

Such are the vagaries of customer support on Twitter. Hailed as the Next Big Thing, customer service through tweets is a work in progress, says Pete Blackshaw, executive vice president of digital strategic services at Nielsen. The performance of many companies has been uneven as they try to handle a crush of customer queries, integrate Twitter into their overall strategy and manage the heightened expectations of consumers.

"Social media is not a panacea," says Blackshaw. "It is a catalyst for fresh thinking on how companies can improve customer service in the digital age."

More than half of the Fortune 100 companies are using Twitter for customer service, recruiting employees, blasting news and announcing promotions, according to the study by public relations firm Burson-Marsteller and its digital-media unit, Proof. Yet a recent Deloitte survey concludes that organizations continue to struggle to harness social media's full potential.

The 'Instant Gratification' Trap

"Companies go in with expectations too high, and they risk disappointing customers who don't get prompt replies," says Lloyd Trufelman, president of Trylon...