For those on the job hunt Twitter can be a great research tool. You can find jobs. Good resource for that is TweetMyJobs.com. It is a great way to find those working at a company you are interested. You can find out a little bit about the personalities at the company, and what sort of things the company tweets about.
Want a little FAQ go to Twitters site: https://support.twitter.com/entries/13920-frequently-asked-questions