Some bloggers that deem themselves successful think that the bad ones are doing a disservice by existing. I don't believe this, but I am obviously biased. First of all, my Google searches are not filled up with irrelevant personal anecdotes. so I do not see how anyone suffers because people like me make their hatred of whole wheat lean pockets public. Secondly, these blogs serve a similar purpose as a journal does to the writer. I say similar because as I recently realized there is a different between a public blog and a private journal.
I'm rather straightforward in this blog, but not because I hide under the blanket of anonymity. A quick Google search of my handle will turn up my real name and my email address. Because of this, there are certain things I won't say for various reasons. These are not of the secrets I will take to my grave variety. They are more along the lines of things I'd rather not let certain people know. Many of them I have no problem with letting most of my friends and total strangers know. It would just be for the best if certain other people didn't know.
An example of information I previously wanted to keep secret from certain parties is I quite my job as a customer service representative for an ISP to work for a company that printed t-shirts as a programmer. Except for the first couple of months at the new job I worked weekends at the old job. Now I probably would not be fired for having a second job, but its generally not something looked upon in a positive light. This is especially true when you are a salaried employee. At this point in time I no longer work for either party so I don't mind sharing this fact.
At the time I did note in my myspace blog that I was moonlighting, and my new coworkers found me and my blog with my little secret. In the end nothing came of it, but it was stupid on my part.
So your potential audience affects what you say. While in general I may write the same sort of things in this blog as I would in a journal, some things are said differently because others might see them. The same could be said for a journal I intend no one but myself to see as opposed to one I would allow others to see.
In my case that means certain things are not said, Also, I make an attempt to make events sound more interesting since I potentially have an audience. In that regard I find this blog a better tool for improving my writing than a journal. The hope that random people will find me interesting enough to read me regularly makes me want to say something interesting.