Ice breakerGMail's arrange-mails-by-conversation feature has always impressed me. In the normal case of a thread being involved (you reply to a mail, forward the mail without changing the subject etc), they seem to club together mails correctly. This is pretty easy to do of course.
But they also seem to doing more than just using the headers to figure out the conversation list. I think there's a temporal window involved as well. So today I simply sent a mail to myself with a subject line identical to another mail I sent out earlier the same day. GMail added this to the old conversation. I tried with a subject line identical to a much older mail (a gap of about 70 days) and it didn't put the new mail under that conversation.
Now interestingly, a couple of months ago, two mails from two different people with the same subject line but apart by 3 days ended up together. So the algorithm is a little naive, for even a simple similarity match between the bodies of the two emails would have told them apart. Perhaps the mails fell in some boundary condition.
This was the first time this happened to me, so was wondering if anyone else had seen something like this in their GMail inboxes.
Update: Useful link on the topic thanks to a comment from IndianPad.