Update: This post has also been superseded - new comments belong in the latest thread.

The second thread has now also exceeded 500 comments, so after 42 chapters of MoR it's time for a new thread.

From the first thread: 

Spoiler Warning:  this thread contains unrot13'd spoilers for Harry Potter and the Methods of Rationality up to the current chapter and for the original Harry Potter series.  Please continue to use rot13 for spoilers to other works of fiction, or if you have insider knowledge of future chapters of Harry Potter and the Methods of Rationality.

A suggestion: mention at the top of your comment which chapter you're commenting on, or what chapter you're up to, so that people can understand the context of your comment even after more chapters have been posted.  This can also help people avoid reading spoilers for a new chapter before they realize that there is a new chapter.