Many bloggers and, in particular, users of Twitter are taking advantage of URL-shortening services. Web sites such as TinyURL and Bit.ly allow users to take a long URL and effectively shorten it by creating an alias.
This is a handy, space-saving convenience for users of Twitter where messages are normally restricted to 140 characters. The bad guys, however, are also free to use these services, and are doing so in order to hide the actual URLs for malicious sites. To combat this, TinyURL and Bit.ly will allow you to preview the actual URL behind the alias before you click on the shortened link.
As always, be careful where you click.