I can remember the moment when I first signed up for a Twitter account.
It was December of 2009 and I was attending the Do It With Drupal conference in New Orleans, LA and one of the speakers was talking about keeping up with event details and postings via Twitter. They encouraged us to sign up if we had not yet created an account and I did it.
At first it seemed a bit silly, but after a few days, I was starting to get the hang of it.
Now that it is 4.5 years later, I wouldn't say that I'm a pro at Twitter, but I have a much better grasp of how to use it and how to get a better experience from the tool.