Private blogs are here! You can go to Settings > Privacy in your dashboard, then select one of the bottom three options if you want to lock your blog from the public. The first option isn’t much, as anyone can register, but for the second, you get to pick who and only who can view it, under Users. The third one isn’t much use, because I’m the only administrator. So if you want to make your blog private, you’ll be using the “I would like my blog to be visible only to registered subscribers of this blog” setting. I tested it, and you don’t appear anywhere; not in the recent comments, blogs, posts, or search. This is great if you need to write just for your friends, family, or some secret group. It locks out the community, so I don’t recommend it otherwise.
Thanks to the More Privacy Options add-on for these enhancements. 
