It doesn’t happen too much anymore, but in the earlier days of browsers they would crash far too often, and I consequently lost what I was working on. I remember several occasions when I was writing a long e-mail and the browser crashed and I had to write it all over again. Another time I was writing a blog entry and was looking at another site to do some research when the site caused the browser to crash, leaving me with nothing but a blank screen and lost time.
Word Processors solved this problem ages ago, and I’m surprised web browsers haven’t followed suit. The solution is to periodically cache any user-entered data. That way, if the browser crashes, the data from the last backup is restored and instead of losing the entire thing, you only lose what you typed since the last backup. Firefox would need to start restoring tabs (or maybe the feature could be added to the Session Saver extension) but Opera already saves sessions, so all that’s left there is to repopulate the fields. There are probably some complexities that I’m not thinking of that the developers would have to overcome, but I for one think it would be a very useful feature.