As a network, Yahoo websites are the second-most trafficked behind Google according to comScore’s numbers. Yahoo’s properties are diverse and Yahoo is far closer to being a ‘media‘ network than Google.

Yahoo’s impressive audience of over 145 million visitors in January is one of the reasons that many have high hopes for a turnaround. But what assets should the company focus most on leveraging?

If traffic numbers don’t lie, Yahoo’s turnaround could be dependent upon what it is able to do with Yahoo Mail. According to Hitwise, 36.71% of Yahoo’s traffic comes from Yahoo Mail. It’s the most popular email service in the US and took in 56% of total visits to email services in February, handily beating Windows Live Mail and Gmail.

Yet a free email service might just be one of the less desirable assets to build on if you’re Yahoo. After all, there’s only so much you can do with free webmail, right?

To her credit, Yahoo’s new CEO Carol Bartz recognizes how important Yahoo Mail is to the company and its future. As reported by ZDNet’s Larry Dignan, Bartz told attendees at the Morgan Stanley Technology Conference that Yahoo Mail was increasingly important to the company and that it would be working on ways to better enable photo sharing and other such services.

Yahoo Mail is the company’s key bond with many members of its audience and many observers thought it could play a key role in helping Yahoo create a massive social network of its own, something it never succeeded with. It will be able to see if Bartz is able to take Yahoo’s webmail domination and turn it into a competitive advantage.