Based on a couple of reports from students and my own experience just now, TypePad is currently generating a random error message when people attempt to leave comments on the blog.
The message reads: "Your comment could not be posted. Error type: Can't locate object method 'log_user_activity' via package 'PhenoType View'", and will appear after doing the captcha code and hitting "post".
However, before retrying your comment, hit refresh. The error message should go away and your comment should appear. If that does not seem to work, hit refresh again and/or return to the blog homepage before returning to comments on the post to which you are trying to respond. Your comment should eventually appear.
I will monitor this problem and let you when it goes away or if comments really do begin to be blocked.