Personally I think it depends on the type of blog you're running. If you're running a blog where you're purely giving information, nothing else, I recommend writing a bit about the subject and how brilliant your site is at delivering content on that subject.
If, however, you're running a site where you are connecting with the readers and that sort of thing (which you should try to do), I recommend an about page where you talk more about yourself.
Here's my about page, if anyone's interested... I recently spent some time making it a bit better: