I've been keeping track of these things, and it appears the number of blogs that ping the aggregators are growing at a rate of about 10,000 per day.
This is important for you to know, especially for those who've set up a blog and been disappointed by the readership.
Two questions to ask yourself --
1.) Do you ping? If you don't understand the term, then it probably means your blog isn't announcing itself. If you're with a blog platform such as Blog City, well, they don't ping. It must be done manually. Some people decide it's just too much trouble. But that's for you to decide.
2.) Can you wait a couple weeks? If you're pinging and listing yourself every time you see a blog directory, then you will see visitors. That's if your content is worthwhile. If the content of your blog is so-so, then they won't come back; same as with a static website.
Don't be put off by the numbers of blogs that keep being reported -- right now I'm hearing four million. This is no big, because most of them don't ping. If you want to be noticed, make sure you've got an RSS feed and there's some way, either manual or automatic, that your blog is getting that ping with every new post.
So far this is the only "secret" of blogging I've discovered. But it is vitally important if you want new readership.