As far as I understand, there are two kinds of blogs: successful ones and the rest. :)
On top of that, all sorts of advisers on the web (what else would they be doing?) often advise choosing a narrow niche for your blog and writing about one topic only, one you know well, say.
I see the sense in that advice, especially for a standalone blog rather than one on LiveJournal. On the other hand, I want to prove the opposite and make a good (interesting) personal blog, because I want to write about all sorts of things, not only about neuromarketing, say. Comrade Davydov, for one, started out writing about marketing, but gradually moved on to general business topics and more and more often writes about economics, which is very interesting too.
Maybe the point is that a successful personal blog takes a good author, while a niche one often takes just a good copy-paster?