I think Facebook should have an autosave function on its messages.
As a teenager I had a number of horrifying moments where I lost huge portions of important school or university work because of computer malfunctions, and now in the age of the cloud I'd kind of thought it would never happen again.
I'm used to working with Google tools, most of which autosave your work (certainly Gmail and Google Docs do) and I suppose I'm getting used to a world where you don't have to constantly save your work for fear of a crash.
For many (not me), Facebook is replacing email as the primary way of communicating online. This is why I find it strange (and frustrating) that it does not autosave as you type.
Come to think of it, does Facebook have a 'save draft' facility at all? It should.