I just noticed this on a recent WordPress.com blog entry:
Update (May 17): Since this feature went live we’ve had a bunch of feedback and it looks like following comments by default is not a good fit for a lot of bloggers (and their readers) after all. We looked at a few different options, but for now we’ve just changed things back to how they were before. To follow a conversation, make sure you check the box when you post a comment.
I complained both here and in a support ticket when this change was originally made, and I just wanted to say thank you for changing it back.
The blog I need help with is unlikelyexplanations.com.