I edit posts extensively before submitting, so I frequently see "Unknown or expired link."
This error is a minor tax on carefully worded, carefully considered posts. I've lost posts following this error due to back button/refresh mishaps. I could post, then edit, but then people are voting and replying to content that is changing.
PG recently suggested that just going back recovers the composed comment. However, here's a reasonable sequence of events which, in Firefox, causes unrecoverable loss of a submitted reply:
(1) open the 'reply' link in a new tab
(2) compose the reply
(3) submit, getting the 'unknown of expired link' error
(4) go back -- you still have your comment, but...
(5) hit reload, figuring that will refresh your reply form's fnid validity -- after all, this works when commenting at an article's top level
(6) get the "unknown or expired link" error now on the reload, with no place to go further "back" to, and "forward" just leading to the same error. Your comment is unrecoverably lost.
I'm now in the habit of a textarea "select-all, copy" before ever hitting a submit button at News.YC. Thus, I can reclick a path from a fnid-less URL to a new reply box if necessary. But that's a pretty user-hostile workaround to expect of people.
Also a nice (although minor) feature would be to add a link back to news.yc when the expired link error occurs.
It's not that important but it would be nice not to have to delete the url parameters in order to get back (or find the bookmark again)
What was changed recently in this department ? I know the timeout was increased, but I used to be able to work around the "expired link" message by going back to the "Add Comment" form and refreshing the page. Now this also yields "expired link" and destroys the post text in the process ! I just lost good 30+ minutes of typing, and I ain't going to re-type it, so it is everyone loss .. :)
Please do something about this, it was a minor annoyance before, but now it turned into a pretty major headache.
Also, the 'Preview' button would be very nice to have. I know there's a delay setting, but that's not it. I want an ability to privately preview what I've wrote, before posting anything.