Personally, I'm not seeing the value of the numbers.
You lose the threading anyway.
Yes, gmail doesn't thread properly. People need to complain to them.
they group a conversation by the Subject. and since we change the
subject with each message, it's toast.
but werewolf (not sure about werewolfbite, but...) tries to maintain the
"In-Reply-To" headers and the corresponding message ids.
If I reply to this message, I'll be attached at the head of the threads.
Not after some random comment from later on.