Social media has added many new marketing channels to our toolbox: blogs, forums, user-generated videos, social networking sites and so on. But none of them is as odd as Twitter.

Think of Twitter as something between microblogging and sending public instant messages. People post very short messages (a limit of 140 characters) called "tweets" about what they're doing or what they're thinking, and other people follow their every word. As with blogs, individuals are using Twitter to stay in touch with friends, to rant, to ponder, to experiment, to brag and (from many tweets I've read) to avoid boredom.

Why does this matter to marketers? Because Twitter is becoming an increasingly important platform for online communication and conversation. Numbers are hard to come by, but TechCrunch reports that Twitter has more than 1 million users (200,000 of which are active every week), and about 3 million messages are posted every day. These are still relatively small numbers, but the activity comes from an early-adopter segment that can be hard to reach using traditional marketing channels.

Where there's an emerging communications channel, there are always marketers fearlessly jumping in, and the same is true of Twitter. Who's doing it well? How can you use Twitter for marketing your products or services? What are effective ways of engaging in this emerging dialogue without turning people off?

Here are five core ways to dive in.