I would say even earlier than 2008, at least if my memory is not betraying me.

I guess it depends of your definition of blog, but I remember Fotolog being incredibly popular circa 2006 even when compared to mainstream social networks. While Wikipedia says it's a social network, I recall it was used mostly for blogging (not so much for social interaction).

And IIRC, when Google acquired Blogger (2003) blogging was not exactly a obscure thing, although I don't think I knew anyone with a personal blog back then.