Often I avoid clicking on shortened URLs because I don't know where they will take me, especially if they are from someone I don't know.
These Chrome extensions for bit.ly and goo.gl will reveal the full URLs when you hover over the shortened URLs.
Bit.ly also has an official extension for Firefox.
[crarko adds: I tested this, and it works as described.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=201103110522076