I don't blog, but I keep a personal and business journal (don't want everyone to know what I'm thinking) but blogging in something that should be done out of passion at the first place and the profit motive at the second place or further down.
To earn serious bucks with blogging you need a lot of traffic and for that you need good content, I'm not talking about a well written article on something, I mean content that is the best on the web, something that people actually want to read and find useful.
If you're in it for the money, start 10 micro-niche sites and rank them, much easier than earning money with blogging.