Whether you're presenting at a national conference or in a nondescript conference room, your audience might be larger - and more opinionated - than you think.

Increasingly audiences are using the social networking site Twitter.com during live presentations to make comments about how the speaker is doing, says Los Angeles business consultant Cliff Atkinson, who writes about this phenomenon in his book, "The Backchannel" (New Riders, 2010).

These days when you present, your audience likely has its own audience.

Live Tweeters can raise a speaker's stature by instantly posting nuggets online. And just as quickly, they can undermine a speaker's credibility. For example, Tweeters ridiculed the keynote speaker at a higher education conference for using yellow font on a white background and challenged his credentials as a social media expert, Atkinson says.

This backchannel can be distracting, but it helps speakers meet audience expectations. Going forward, savvy presenters will monitor Tweets and take "Twitter breaks" to encourage online discussion and address any concerns, Atkinson says. Catering to the unseen audience, speakers will sum up important points in fewer than 140 characters - the maximum length for a Tweet.