On Stack Overflow, there are many questions that relate to currently-developing technologies such as HTML5 and CSS3. The accepted answers to these questions may become outdated, and better answers may appear. However, because the answers are accepted, it is likely that they will continue to be upvoted by users reading the answers, and the OP will likely not notice that a better, more up-to-date answer may exist.
Should these outdated answers be voted down? If not, what should we do with them?
No, that's rude. You can at least post a comment to the answer and give people a chance to improve their answer if something has changed. Or, better yet, just post the updated information in the comment. Or... even better, edit the information straight into the answer! That's why this is a community editable place. Information does change.
If you're really greedy for reputation: sure, you can post your own "updated" answer, but surely don't downvote other people just because their answer is out-of-date. No one goes through all their answers to find the ones that need updated with new information.
Anyone can look at the date the answer was last updated and logically figure out "hey, this was posted a year ago, maybe something else has happened since then."
This answer of mine stating that a specific CSS function cannot be done at this time will eventually become outdated, whenever CSS4 is officially released and becomes supported in browsers. However, it will still always be "correct" in the context of the question, because at the time we were stuck with CSS3 which didn't support that functionality. Since this question specifically refers to CSS3 in the text, submitting a new answer wouldn't be appropriate, but it's always nice to add a simple comment noting that the functionality is now supported, whenever that comes to be.
Or, see the comments below for other examples.
If information changed (e.g. a fact was since proven incorrect) then, sure. We're not here to be polite or rude but to share knowledge, and if the knowledge presented is incorrect then that's the way it is. It would be nice to write a comment, though, to indicate to the OP that their previously-correct answer may no longer be accurate, and informing them of the downvote.
But this is not the same thing as downvoting a correct answer that relates to old technology just because new technology has arrived. If the answer is ambiguous, feel free to comment on it along the lines of:
Note: This answer relates to an old version of
$technology. Versions released since fix this bug.
