I asked a question about vim in the ubuntu stackexchange, and someone suggested it should be taken to stack overflow or superuser.
Would this be relevant, or should general Linux/UNIX software stuff be taken elsewhere?
I don't really think general Linux/Unix questions should be excluded from the Ubuntu StackExchange. I really think anything related to Ubuntu at all, no matter how general should be accepted.
Sure they can go to the Linux StackExchange when thats up or SuperUser but really they are going to be asked here anyways by someone eventually, its inevitable. This is the whole problem with questions that can go on more than one site, not everyone can get it right as to where its supposed to go. And these other sites, it isn't always obvious that they exist.
A Ubuntu user might look here for an answer to the vim question and not know about Super User or the Linux Stack Exchange, as they are completly seperate sites. Or maybe they just dont want to do this whole signing up to 10 different sites and hopping between them. So far as I know there is no inter-site search yet that isn't Google so searching isnt exactly a breeze either.
I would ask a vim question here opposed to anywhere else more because I want a Ubuntu specific answer. I don't care if RedHat or another disto does it differently or the same. I dont want to get an answer for another distro that ends up being completly different for Ubuntu. I want the answer from a Ubuntu user, for a Ubuntu user.
If we draw the line at only Ubuntu applications and Ubuntu UI, users are going to drop off for other sites that have a more complete Question/Answer base. On the flip side that could be fine, it concentrates the questions more. But it also just makes it less complete of a resource.
So my opinion is anything that has to do with Ubuntu at all is fine.
General Linux/UNIX (seriously, are you asking if UNIX questions should be posted on Ubuntu StackExchange?) question should be posted on https://superuser.com/ or the Linux StackExchange.
A good rule of thumb (for now) is that questions involving Ubuntu UI (e.g. applications, desktop shell) or community should be posted here; questions that do not relate to Ubuntu UI or the Ubuntu community should go elsewhere.
Ubuntu is one of the most popular Linux distribution over the world. So there may be some general questions relevant to any Debian based Linux distro. But that does not mean he/she can't post it here. Because if it is a general question for Debian based distro there will be a 90% probability that ubuntu also have the same question.