Take a look at the Daily Pageviews graph below.
In just one short month Bit.ly has gone from having 1/3 of the pageviews of Tinyurl to having 30% more.When it comes to pageviews, Bit.ly is now king of the hill.
When it comes to visitors, Tinyurl still wins, but not for long. Alexa's Daily Reach graph indicates a steady decline in Tinyurl visitors and a meteoric rise for Bit.ly. In just two more weeks Bit.ly will take over to become the undisputed king of the URL shortening hill.
I am not acquainted with the details of the deal between Twitter and Bit.ly, or the reasons behind the switch from Tinyurl, but I am certain of this. This seemingly minor change represents a big deal to both Tinyurl and Bit.ly.