Last week's launch of Facebook Groups resulted in the inexplicable disappearance of "Clear Chat History" button from Facebook Chat. According to sources "button's removal was due to load issues cause by new reliance on Group chats, as chat data greater that 14 days would have to make a database hit, overloading the server if scaled to apply to large Groups and causing performance issues."
However, a group of Facebook users protested, despite above cited concerns, Facebook responded:
We've been making a number of changes to optimize and simplify Facebook Chat over past weeks. As part of the effort to improve Chat, we've been testing an interface without the "clear chat history" link prominently displayed, since only a small number of people use it.
Based on tests, we've decided to keep "clear chat history" and to optimize it's placement within Chat interface. We're placing it at the top of Chat scroll ? where it's still easily accessible without cluttering UI space throughout the course of chat. We believe this solution strikes a good balance between many different interests of the millions of people on Facebook Chat.