Take this post on how to make the most of your social networking accounts. The gist is:
First, it enlarges your Internet footprint. The more places you are, the more people are likely to find you.But he has a lot more wisdom to dispense than just that. Not only in that post, but in the entire blog. I'll be linking to him some more in the next couple of days so that I can find certain posts again later.
Second, it makes it easier for people to stay connected to you. The more you remain in the forefront of people's minds, the better off your brand is.