Structured data helps Google Bot and other web crawlers to understand and interpret your data. By tagging your data with structured data tags like MicroFormats h-entry Google can index all relevant information. The tags also affects your search appearance, i.e. what your site looks like in the Google search results. You can also be sure that this will effect your page rank!
If you haven't already got Google Webmaster Tools up and running for your site, now is a good time. There you can check how Google interprets your tagging. Google haven't released a list of things that effects your page rank, and probably never will. It is pretty obvious that Google take this kind of tagging into the page rank. I draw this conclusion because it is included in Google Webmaster Tools and it will also report errors in the tagging.
Microformats is an extension on HTML/HTML5 witch makes it pretty easy to tag content via the class attribute. The div containing the blog post has class="hentry" set. The reason why this is used instead of the new h-entry standard is that the WordPress post_class() function ads hentry instead of h-entry as a class.
<h1 class="entry-title"> <a title="Amazon AWS EC2 Linux Swapfile" href="http://www.hackviking.com/2014/09/amazon-aws-ec2-linux-swapfile/" rel="bookmark"> Amazon AWS EC2 Linux Swapfile </a> </h1>
Inside the div containing the blog post we first have the heading. By setting the "entry-title" class for the h1 you have successfully tagged the title so the Google Bot can pick it up. By setting the rel="bookmark" on the link back to it self you have accomplished to get the bookmark in there as well. I like to use h1 both for site title and entry title. According to Google Webmaster Blog this is alright as long as you don't overuse it. Watch the video at the bottom for more information.
<span class="published"> <span class="value-title" title="2014-09-04 10:18:02"></span> </span> <span class="updated"> <span class="value-title" title="2014-09-17 12:27:23"></span> </span>
When displaying published date and time you probably want to use something sexier then 2014-09-04 10 10:18:02. So just add these span with the correct classes attached and there will also be tagged correctly.
The author vcard is an other standard error most sites have. It isn't harder then adding markup like this:
<div class="about_author vcard author"> <h4>Posted by <a href="http://www.hackviking.com "><span class="fn">Kristofer Källsbo</span></a></h4> </div>
The author and vcard classes on the outer container and then a simple span with the class fn witch stands for full name and you are done with that error as well.
This is article only scratches the surface of what you can do with the markup! I addressed the most basic errors that most blogs get when they check this out for the first time. You should really use the Google Webmaster Tools to verify that Google reads your site the way you want. There are several good tools in there especially for testing markup and verifying that your site has the correct one or at least one that Google can read properly.