Of course, just because you mention a company doesn't mean that it will respond or acknowledge your Tweet.

"Using tools such as Sysomos and HootSuite, we can see just about any public Tweet that mentions our name, tagged or not," says Julie Jarratt, sponsorship PR manager at Esurance ().

"If we're not tagged, it could be seen as intrusive if we respond to the user. But at the end of the day, [how we react] depends on the context of the Tweet. If it seems like they're having an issue that needs our attention but we haven't been tagged, we'll respond," Jarratt says.

Companies also use Twitter to stay on top of trends affecting their customers.

"From a data standpoint, we're able to get an instant pulse on what consumers are trying to accomplish at any given moment," Best Buy's Bernier says. "And we can identify pain points in that process."