I have recently had this error message when submitting comments on on of my clients sites:
"Unmatched ) in regex; marked by <-- HERE in m/24.116.204.32) <-- HERE /..."

It occurs here, if you need clarification:
http://www.bloggerheads.com/mt/mt-comments.pl

Can anyone shed light on this? The site has typekey enabled, and has previously worked fine. There have been no server updates to my knowledge.