Recently twitter moved from automaticlly shortening urls with tinyurl to shortening them with bit.ly.  There are probably several reasons behind this.  One of the largest factors is that twitter users enjoy their stats!  With tinyurl, you would always have to use a secondary program to count clicks.  Not only did this take up time, but it really was annoying.  Also, tinyurl was not as short as shortening urls come.  Bit.ly helped people shorten their url even further, allowing for larger amount of customized text in the tweet.  Twitter and Google have recently announced the possibility of including twitter links in the google search results.  This would be amazing as Twitter is used by so many tech savvy people.  The data possibilities with these shorter links is just an amazing thought!  Bit.ly is a fast growing url shortening service, in fact now the top over tinyurl!  The stats and other advantages to Bit.ly will make sure that it stays on top for at least a few more weeks, if not forever!