URL shorteners are a plague on the web. They serve no purpose other than to create a short link to be able to send a longer url via some limited channel (email, chat, sms, twitter, other mobile services) to a recipient.
Partly to blame are CMSs that output urls that are simply way too long.
But URL shorteners are not a solution, they’re a problem in their own right.
If a url shortener goes down (see vb.ly) for whatever reason then immediately there is a gaping hole in the web because these short, throwaway urls have a habit of nestling just about everywhere they shouldn’t be seen.
They are effectively nothing more than a mapping from one URL to another, and so they add another layer of indirection that can fail to the process of clicking a link.
They hide what that link actually points to (with lots of creative potential, as well as abusive potential) and they make it harder to create a graph of the web.
So, down with URL shorteners. Do not allow your users to post ‘short’ links, and if they do replace them with the original link. Add a canonical ‘short’ link to your pages that is tied in closely with your CMS if you have to. That way users don’t need to resort to external URL shorteners. If you run a service that displays URLs to customers and you do allow short links provide the original link as an option next to the short link if the display medium is capable of doing so.
That way the short link madness gets curbed at a manageable level and any damage from short link providers can be limited.