The social media phenomenon known as Twitter saw a marked increase in users in 2009. It seems everyone and their aunt is on Twitter these days tweeting about anything and everything. What I find interesting is the number of marketers that have found ways to sell this as an advertising resource for their clients. According to Jack Marshall of ClickZ, Twitter will need to back up their buzz in the new year with some real return on investment info for clientele that use the microblog for advertising. Tweet that.