I am very excited to say you that you can now create your own short url serivice... So, why we will go for such short url services like tinyurl, bit.ly and others.
The short url service of your own domain can increase your traffic as well as can place a good impression to the real time search users... It may come that the Twitter users starts using your short url service if they found your url more catchy than others.
A script by YOURLS , gives you the personal (private) or commercial (open to public) URL shortener for free. The script requires a server with PHP 4.3, MYSQL 4.1 and mod_rewrite enabled.
A Step by Step guideline by ShoutMeLoud to create your own URL shortening service. Follow its guidelines install it on your server.