The number of topics we choose to blog on in any blog is unlimited. Personal blogs are more likely to be succesful if the blogger choses a minimal number of broad categories that relflect their primary interests. Then provided the architecture of the blog is well organized, basic SEO is used, and relevant categories and tags used are clearly defined, the indexed posts will atract readers who use search engines to type in the same keywords as were used by the blogger.
The personal blog, an ongoing diary or commentary by an individual, is the traditional, most common blog. Personal bloggers usually take pride in their blog posts, even if their blog is never read. Blogs often become more than a way to just communicate; they become a way to reflect on life, or works of art. Blogging can have a sentimental quality. Few personal blogs rise to fame and the mainstream, but some personal blogs quickly garner an extensive following. http://en.wikipedia.org/wiki/Blog