The thought has struck my mind on more than one occasion. The reason why I don't do it is because 1) it will take too much of my time and 2) I think my life is way too boring to be of interest of anyone. You really need an extraordinary life in order for anybody to care. And not only that. You also need to be great at formulating thoughts about it. 3) I also would need to make something off it. Not necesarily money directly, But there must be some gain for me.
The only real losers in the world are the ones who never try, so good luck to anybody who does.
edit: I read a report today saying that the number of blogs in 2007 compared to 2006 is 100 million less. Too me that's a mind-bogling number. I have a feeling people write more blogs than there's people reading them.