Technorati's front page sez:
5,007,602 weblogs watched[HT, Instapundit]
Some days, I visit more than that.
[NOTE: The commenter pointed out that the title had indicated 5-billion blogs. Thank you for the heads-up, and I've fixed it.]
It's 5 million, I believe, which is what you say in the post, not 5 billion, which is what you say in the post's title.