I started using Twitter because of Twitterrific for Mac. When the Iconfactory first released the app, I signed up for a Twitter account and started chatting with my friends. That was ten years ago.
Ditto. I actually started using Twitter via SMS in 2006 then saw it bloom at SXSW in 2007 but then when I saw Twitterrific in 2007-2008 it became a daily (heck, hour-by-hour) habit.