Googley's solution is probably the easiest one.

The browsers I'm using now (various versions of Firefox) are good at letting me back up to something I was writing. I've even had the power go out for an hour and still been able to recover a post afterwards.

When I was using earlier, more primitive browsers I learned a couple of other ways to avoid losing posts:

1. Before submitting a longish post, save a copy to a file with Windows Notepad or a word processor. You could even write the post in a word processor before submitting it but you wouldn't have easy access to the BB Code formatting tags that way.

2. If you think you may have been logged out, open a Forums page in another window or tab. Once you're sure you're logged in, then go back to your post and submit it.