I've actually been conditioned so thoroughly by flaky forum software to ctrl-a-c on every post before submit that I don't even think about it and sometimes I'm surprised when I paste later and get whacked with a giant forum post.
I also do this. Not just on forums, but on pretty much anything where I write a decent amount of text. I also use a clipboard manager in conjunction with this habit (http://itunes.apple.com/us/app/clipboard-history/id420939835...) that has saved my ass numerous times.
I have dealt with this a number of times, and any time I think I am going to write a comment that is more than a few lines long and has any real significance to me, I do it in a word processor or full text editor where I can easily review it and spell check it before posting.
Or losing half the fields due to a validation error, which then creates other validation errors when you re-submit. "Oops! Your password contains illegal characters. Please select a new password. (submit) Oops! Please select a state from the dropdown menu."
I recently purchased new insurance. One company's site created its own scrolling widget for drop downs. Not sure why, but each page had several of these devil widgets.
If you spun the mouse wheel every single custom scroll widget would rapidly change value! Things like jumping from "Single" to "Divorced." I ended up just dropping them from my comparison because I was so unsure of the data I had provided them.
There are straight forward workarounds for this problem. The password field is typically obscured anyway, so the user doesn't see the characters in the field. When a user submits a form where they are asked for a password and a confirmation, you can temporarily persist that data on the server side, linking it to the user's session. You then send a dummy string to the client that matches the length of their supplied password, so that A) the user doesn't have to re-fill your password & confirmation, and B) the raw password data is not sent back to the client.
Good implementations of this approach also don't persist the password in plain-text in the temporary store. You crypt the password using whatever method you were going to when you stored it in the database and keep that around until you're ready to make the changes permanent.
If filling the password in will result in plain text passwords being sent back, you have already lost, because you just submitted a plain text password over HTTP. Similarly, if you're on SSL, it's plain text in neither direction. In either case, sending it back in the form has not changed the security situation.
I'm assuming this is levelled at HN? It's probably the only forum I use regularly where I get timeout's on submission. And the timeout page isn't even friendly either.
HN (and trac) handle the situation best: they don't invalidate the page data, so your post will still be there. You CTRL/CMD A+C then get back to your posting with a refreshed cookie/session.
Many other forums basically wipe out your post, which is highly frustrating.
I experience this from time to time. Sometimes(TM), a single undo in the now-empty field makes all the text reappear. I've recovered many an overly long forum post this way. Try it.
As much as these suck, I can tell you from working on corporate sites that this is often done for security compliance. One site we're working on now has about four different conditions that can expire a session earlier than the user might expect; I can only imagine how irritating this must be for them, and how many sales the company will lose because of it.
I think one of the reasons I stopped using Tumblr for general blogging was because it didn't autosave while I was writing my long posts. I think there are a lot of holes in the walls of houses around the world because of this.
That's actually one of the things Tumblr does right. If you close out of a post before you publish it, you'll get a notice on your dashboard to either continue editing it or discard it.
Another favorite of mine is the forums that have a 'quick reply' box on a thread with a giant "Post Reply" button just above it and a smaller "post quick reply" button at the bottom right.
One of my biggest pet peeves are forms that make you enter your address information, including your "ZIP Code", before asking for your country. Extra annoyance points go to sites that then do a clunky page refresh after selecting a different country and having all of your previous address information disappear into the void.
there's simply no reason why they can't either a) parse the zip code differently based on country, or b) why country isn't listed first if there are uncrossable chasms. To do neither is simply laziness
Some sites you can go back to retrieve your post, others will just present you with a newly empty form.