There is a general opinion among webmasters and bloggers that URL shorteners are evil. As Joshua Schachter, the founder of Delicious, explains:
The worst problem is that shortening services add another layer of indirection to an already creaky system. A regular hyperlink implicates a browser, its DNS resolver, the publisher's DNS server, and the publisher's website. With a shortening service, you're adding something that acts like a third DNS resolver, except one that is assembled out of unvetted PHP and MySQL, without the benevolent oversight of luminaries like Dan Kaminsky and St. Postel.
URL shorteners not only break the whole structure of the web, but the links become dependent upon the continued existence of these third party middlemen. (See VapURL, the disposable URL shortener).
mug.gd is a new URL shortening service that was built to prove how evil URL shorteners can become, if they want to.
mug.gd allows you to shorten a link, and at the same time replace any phrase occurring on the destination page with your own phrase. The service allows you any number of replacements you want.
Clicking on the shortened URL takes the visitor to a page that wraps the original page in a frame with the words and phrases replaced with those of your choice. mug.gd enables you to falsify any page by cleverly replacing words from the original article and an average user won’t even notice the barely visible bar at the top that warns the visitor of the changed content.
Here is an example: http://mug.gd/ExyN
Also read, how to find out the destination before clicking on short URLs and how to edit any webpage.