Twitter is the king of the microblogs.  Their limit of 140 characters per post means that there is a tremendous and constant flow of small bits of information, far more than any one person could ever follow.  They were the first to popularize the #hashtag, a way of tagging posts by putting a keyword behind a pound sign.  This makes it extremely easy to see a constant flow of posts on almost any topic, from real people who have no connection other than a shared interest in the subject of the hashtag.  It’s lead to some very interesting uses in local media, national trends, international revolutions in the middle east, and annoying and forced inclusion in TV news.