URL shorteners were all the rage in 2008 and 2009 – primarily due to the character constraints within the short messages service that was all the rage in 2008 and 2009 – Twitter.
URL shorteners take a long url, for example, this Google Map url:
and transform it into something like: http://tinyurl.com/y3lxdru
Every URL shortener uses their own magic sauce to create the short random string - i.e. the 'y3lxdru' part - and stores right next to the long URL. So if there's a tiny.cc/y3lxdru or a j.mp/y3lxdru - they probably don't point to the same Google Map. In fact, if I understand how bit.ly (aka j.mp) works - their shortened URLs only exist for a few months - and then are 'released' (that's how they're able to keep them short). I even created a automatically expiring URL shortener cause I thought it was funny.
When someone clicks on the short URL, the URL shortener (tinyurl.com in the example above) promises to look up the long URL stored next to the short random string - and promptly redirect you to the location of that Chinese restaurant for your lunch meeting. And not some place unseemly - which has happened, more than once.
There are lots of problems with URL shorteners. I feel qualified to say this because I build 3 of them in the past 2 years (Culld.us, RE07.US, and a native WordPress hack, none of which are currently active).
At best - they make less usable URLs - because both the URLs shorteners domain name and the random string are meaningless (not to mention hard to remember) to people.
At worst - this obfuscation means every short URL clicked is more of a potential computer security risk than normal clicking around the internet.
A 3rd party URL shortener shouldn't be necessary to make Google's Map URLs shareable. Same goes for any other website - URLs can and should be constructed to be reasonably short, human readable, guessable, and accountable. URL design is one of the most under-appreciated aspects of website usability (as is scrolling).
For the past 6 months or so - Twitter has been the only real reason to use a URL shortener. Facebook and other services are now doing a better job of handling long URLs. Many people and companies use URL shorteners as hack for not having a good web site statistics package. Additionally, Twitter has made noises like they're going to default to their own URL shortener in the near future - a move which will promptly shorten the already tiny lifespan of other URL shortening services.