I am relatively new to Ask Ubuntu and stack exchange in general, but I read that x-posting is relatively frowned upon here. Is it acceptable to post a question to another Stack Exchange site, say, Superuser, if the question is not answered here in Ask Ubuntu? What's the best practice for doing so? Should one delete the old question so that it does not show up twice on a search engine?
Cross-posting the same question across StackExchange sites, within a few minutes, definitely seems spammish, to me. If, however, your question hasn't got attention and you can't add more details or raise a bounty for it in Ask Ubuntu, I don't see a problem with it if you can get attention on a more appropriate site.
Personally, I would delete my question here if you were able to get responses elsewhere.
Disregard the previous sentence. In hindsight, it was unnecessary. If you are a regular contributor, here, by all means, I would recommend coming back and answering your own question to add to the AU knowledge-base.
I think that there are good cases to be made for self-deleting one's questions. But, that is probably good for another topic.
We are all volunteers here, so it just may take a while for a question to catch our attention.