This year Yahoo! has been working hard to integrate Facebook in its products – and for good reason, since there are more than 400 million registered Facebook users out there. Yahoo!’s latest achievement is to deliver the Facebook news feed directly to the Yahoo! Mail inbox.

“I’m thrilled to announce another new integration launching to all users that enables you to view, comment, and like your Facebook news feed items – all right from Yahoo! Mail. Facebook activity from your friends will now appear in your Updates section, alongside your friends’ activity on Yahoo!, Twitter, Flickr and so on. Now you can get all your Updates in one place, right when you log in to Yahoo! Mail,” said Front End Engineer with Yahoo! Mail, Tony Cheng.

By default, all Yahoo! and Facebook updates are displayed mingled together in one place. If you find this distracting, you can filter updates. You can select to view only Yahoo! updates or only Facebook updates. Whenever you get a new update, a “Show new updates” link shows up; click it and you will see the new update, without having to refresh the browser.

You can like or comment news feed items in Yahoo! Mail straight from your inbox. The comment will be delivered by Yahoo! to Facebook, so that everyone can see it.

Here’s a refresher on the story of how Yahoo! integrates Facebook into its online properties. Back in December 2009, Yahoo!’s Vice President of Communities, Jim Stoneham announced that in 2010 Yahoo! will be deeply integrating Facebook Connect across its properties. So far we’ve seen the following:

• The option to import the email addresses of all your Facebook friends to your Yahoo! Contacts list. This functionality makes it easy to stay in touch with the people you care about (read more about it here).
• The option to update your Facebook status directly from Yahoo! Mail. Also, when you receive an email from one of your Facebook friends, you’ll be able to see that friend’s Facebook profile photos (read more about it here).
• Comment or ‘Like’ Updates that you see on the What’s New page in Yahoo! Mail (read more about it here).
• Yahoo! Contacts automatically gets filled with info from Facebook (read more about it here).

Please note that you must first link your Facebook account with your Yahoo! Mail account to benefit from any Facebook-related feature. A detailed explanation on how to do so is available here.

In related news, it has recently come to ligh that Yahoo! Mail, fights spam harder, smarter and better than any similar service out there – definitely better than Hotmail and Gmail. As research performed by the Fraunhofer Institute revealed, Yahoo! Mail users saw 40% less spam than hotmail users and 55% less spam than Gmail users.