There’s an excellent essay at the link above about things that bloggers should _not_ blog about. I’ve erred into a couple of those things myself, but have since made a concerted effort to avoid doing so again. My policy for blogging has always been to share the things I’m learning or find interesting and communicating those things to others who might also benefit from them. I want to be stretched by the things I read, so I want to try to provide the same things for my readers (limited though they may be).
Your blog _is_ your space, and people are free to write about whatever it is they want. But bear in mind your audience. If you wish to expand your readership, part of that process is writing about things that others will find relevant. Mr. Huereca points out some of those things that are not and thus ought to be avoided for the blogger looking to reach their readership.