Blogs on WSO have evolved over time.
WSO blogs were the original kind of blogs, and often had long, intellectual conversations where multiple parties were very involved in the discussion. They were in use from a few years ago until 2005-2006, when they became overrun with lost and found and event advertisements.
In early 2006, Evan Miller and WSO rolled out several new services to fill the various roles that the blogs had taken on. WSO Discussions, including "discussions" and "opinions," replaced the blogs, and separate announcement forums for events, lost and found, and exchanges also appeared. There is also a new kind of WSO Blogs, using WordPress.
Some worried that there were not as many long, heated discussions on the new discussions as there were on the old blogs, but only time will tell whether this is the case.
Also see How to trick out your WSO post.