Twitter is a great social networking tool for instant communication, but it was not set up specifically as a marketing resource, so there are a few things missing in the service when viewed from a marketing perspective. First up, most busy Twitter users follow thousands or tens of thousands of people, so tweets are coming in mass all day long. These scroll by, so most users only see those tweets that go by while they are actively using Twitter, other than those directly to them or private Direct Messages and with all the auto-Direct Messages being slung around, many do not even check their DMs very often.