A study by new URL shortener yi.tl claims that out of the 1002 different URL shorteners created in the past decade, 614 of them no longer exist. The company cites spam as the main reason for sites closing, though I'm sure that Google, Twitter, and Facebook using their own URL shorteners had plenty to do with the end of the shortener boom as well.
"Although URL shorteners have become an intrinsic part of our daily lives on the web, the sector is in a total mess." said Anthony Vader, creator of yi.tl. "Very little money or ability is required to set up a basic URL shortener, which is why there are so many start-ups. However, most offer a very primitive service which is vulnerable to spammers and is often hosted on a shared server. Hosting providers don’t like their servers being used for spam and have forced many URL shorteners to close down."
The nature of URL shortening makes them ideal for spammers and malware spreaders. Because shortened links often don't show a link's real URL, spammers can use a shady URL shortener to trick people into clicking links they would never otherwise click.
Vader also laments the fact that all of these failed services now have non-working links sitting around the internet. "The result is that millions of links across the web are now permanently broken. All the information about where those links pointed to has disappeared," said Vader. It's hard to be too broken up about that fact. Most shortened links are meant for content shared over social networks, which are transitory by nature anyway.
yi.tl has provided a list of active URL shorteners and dead ones, including silly ones such as DwarfURL.com, ICanHaz.com, and Puke.it.