URLs seem to grow longer and longer every year. Part of this is due to domain names getting longer, and a lot of it is due to SEO (search engine optimization) changes. Where we used to use /article/1234 we now use /books/reviews/fiction/fantasy/the_lord_of_the_rings so that search engines can mine the URL for relevance. And then so we can track the source of our traffic, we add some query strings (?utm_source=foo&utm_medium=bar) and we wind up with a long cumbersome URL that's great for machines but arguably not so great for people.
Enter a variety of shortened URL services (http://tinyurl.com/, http://cli.gs/, http://bit.ly/, etc). You paste in a lengthy, search engine friendly URL and get out a short but nonsensical URL. For example, the URL www.itworld.com/hardware/62993/new-mac-mini-image-leaked-let-community-decide becomes http://bit.ly/QGqCT .
Now you might argue that the longer, human readable URL is actually easier to use than the shortened URL, which is just a bunch of random characters, and I'd agree with you. You also might argue that you're not often asked to type in a URL anyway, and I'd agree with you there, too. The biggest value in shortening URLs is when character space is limited, Twitter being an obvious example. When you have 140 characters to work with, shortening a URL is crucial.
There's a danger to short URLs though: you don't know where they go. The ridiculous "rick roll" trend of a few months back used this to great advantage. You'd send a friend at the office a shortened URL saying it went to a great regular expressions tutorial. He'd eagerly click the link, hoping to save the few strands of hair he had left, and instead of finding regexp clarity, suddenly he'd be on YouTube and Rick Astley's "Never Gonna Give You Up" would be blaring from his speakers, attracting the attention and ire of an entire hectare of cubicle farm. Ha! Joke's on him.
And of course that which can be used for dumb jokes can be used for evil. Instead of a rick roll you might find a shortened URL unexpectedly directing you to a malware site or other unsavory and career threatening destination.
So what to do? Do we just refuse to click on shortened URLs? That definitely protects us but it also limits the usefulness of Twitter and other web services. A better solution, for Firefox users at least, is to install the LongURL add-on. Once it is installed, you can hover your mouse cursor over a shortened URL and LongURL will pop up the real destination of the link. No more surprises! If you don't use Firefox, there is also a LongURL website that can accomplish the same thing with a few more steps (copying and pasting the short URL). LongURL says it supports "tinyurl.com, is.gd, ping.fm, ur1.ca, bit.ly, snipurl.com, tweetburner.com, metamark.net, url.ie, x.se, 6url.com, yep.it, piurl.com, and more!"
The LongURL website is also valuable for those of us who use a client to access Twitter. I'm not familiar with every single Twitter client out there, but so far I haven't found one that will preview the destination of a short URL. Twitter client coders, please build in this option! And if you know of a client that supports the functionality please leave a comment and share.
Worrying about where a shortened URL is going to take you is a hassle, to be sure. But winding up with malware on your system (or an unfriendly visit from HR) is worse. When in doubt, check the destination of that short URL before clicking.