The Ideal Tweet is 100 Characters
Twitter’s research indicates 100 characters is “the sweet spot for a tweet,” enjoying a 17% higher engagement rate. Tweets from 71-100 characters also do well probably because they allow room for retweeting and adding brief comments to the original tweet. So say enough to get your point across… but leave room for others to have their say, too.
(via 8 Rules of Success for Social, Email, and Blogs | Inc.com)