Can you unblock people you have put a block on? If so, how?
If you want to block a user, you can do this from an email you get from them. If you wish to unblock somebody, you can click on my account and there is a link to the users you have blocked. If you comment on a blog and it says that the comment will be automatically approved, then you make a comment, only to see screen refresh and say, "Blog comment posted and awaiting approval", then you are blocked.
The passage above is from the post Blogging 101 for Newbies