Persistent room conversations

For a long time I've wanted a room or conversation where the server maintained a chat room buffer, however short [configurable], of the most recent lines. The purpose would be for allowing users to disconnect with their client, and reconnect from another place -- a totally different computer, and have the conversation available to them.

This would allow for more important messages to be sent over IM/chat whereas otherwise people would have to use email (which is what I now end up doing).