It still shouldn't have happened that way, Bill - I'd already increased the timeout to something much closer to 30 minutes, so I'm still hoping to get to the bottom of what you ran into.
Granted, I've worked with computers and software too long to trust them, so, if I know it's going to be a long post, I do tend to follow Tom and Mark's advice and compose it offline, just in case.
Having said that...
As you're composing a post, the text is "Auto Saved" every 60 seconds (that's the default timing anyway.) If your browser crashes or you accidentally close the tab or whatever, the next time you log in to the forums and open the post editor (to create a new thread or reply) you'll see a button at the bottom that reads "Restore AutoSaved Content" - push that, and everything you'd typed as of the last time it saved magically reappears. It's actually a nice little feature.