If you have spent anytime using social media or working with Web 2.0, then you have probably heard of Mashable.com, one of the largest blogs on the Internet dedicated to the subjects. With the recent release of the blog's free official iPhone app Mashable!, fans of the Web site should find keeping up with the latest news and trends that much easier.

Mashable! has a fantastic UI that is both user-friendly and user-intuitive. I love the horizontal-scrolling tabs at the top of the screen, which sorts the site into topics such as "social media," "mobile," "entertainment," "tech" and "Apple." At the bottom, you can choose to narrow your scope further with category filters such as "Facebook" or "celebrities," or with tags such as "Twitter" or "viral video."

The home screen displays the latest news and trending stories, with the newest information appearing at the top. To refresh, users merely need to drag the screen down, which then bounces to refresh, a design that was first seen, and highly lauded, in Tweetie 2. Users will also find access to the site’s search function through the magnifying glass on the top right-hand side.

Once you’re in a story, you’ll see options to share the story via email, Twitter or Facebook, or read the story later through Instapaper. You’ll have to make a trip to the settings panel to enable the integrated Instapaper and Twitter, which currently supports updating via Web, Tweetie, Twitterific, Echofon, Echofon Pro and Twittelator. Tweeting  a story launches your selected Twitter client with the tweet already created, but I don’t love exiting the iPhone app. Videos, however, do launch in-line, as do external links.

There doesn’t seem to be support for landscape reading in Mashable!, but since content is optimized to appear vertically, it’s not a dealbreaker. Really, the only thing the Mashable! iPhone app is missing for me is the ability to read and post comments.