Community and cataloging

The Blogosphere
The collective community of all blogs is known as the blogosphere. Since all blogs are on the internet by definition, they may be seen as interconnected and socially networked, through blogrolls, comments, linkbacks (refbacks, trackbacks or pingbacks) and backlinks. Discussions "in the blogosphere" are occasionally used by the media as a gauge of public opinion on various issues. Because new, untapped communities of bloggers can emerge in the space of a few years, Internet marketers pay close attention to "trends in the blogosphere".
BlogDay
BlogDay was created with the belief that bloggers should have one day dedicated to getting to know other bloggers from other countries and areas of interest. The designated date is August 31, because when written 3108, it resembles the word "Blog". On that day, bloggers recommend five new blogs to their visitors, so that readers discover new, previously unknown blogs.
Blog search engines
Several blog search engines are used to search blog contents, such as Bloglines, BlogScope, and Technorati. Technorati, which is among the most popular blog search engines, provides current information on both popular searches and tags used to categorize blog postings. The research community is working on going beyond simple keyword search, by inventing new ways to navigate through huge amounts of information present in the blogosphere, as demonstrated by projects like BlogScope.
Blogging communities and directories
Several online communities exist that connect people to blogs and bloggers to other bloggers, including BlogCatalog and MyBlogLog.
Interest-specific blogging platforms are also available. For instance, Blogster has a sizable community of political bloggers among its members.
Blogging and advertising
It is common for blogs to feature advertisements either to financially benefit the blogger or to promote the blogger's favorite causes. The popularity of blogs has also given rise to "fake blogs" in which a company will create a fictional blog as a marketing tool to promote a product.

source:Wikepedia