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.
