This idea has come up, and been rejected, many, many times. Just one such discussion is located at A Chatterbox Archive. The fact is, people may say things in the Chatterbox that they'd rather not have archived for posterity. The chatterbox is an informal setting where people can say things without having to worry about them being logged and brought up again later. That doesn't mean I advocate offensive or obnoxious chatter, but the fact is that many people will modify their behavior, even if it's perfectly innocent behavior, if they know they're being watched and recorded. Logging the chatterbox will likely cause people to become more guarded in what they say, and thus will remove much of its charm. I know you're saying only the last 10 messages or so, but the same principle applies.
in reply to Chatterbox rewind feature?