I use SteamOS and am having a problem with it, but I don't know whether or not to mention it in Ask Ubuntu.
It uses the .deb files, so it is quite similar. Should I bring it up, or not?
SteamOS in general no, but there is a way to install a "SteamOS login" within ubuntu - http://www.webupd8.org/2013/12/install-steamos-session-in-ubuntu.html but basically this breaks stuff... since not supported + questions about bugs.
This also leads to "drive by" answers, commenting on how things shoud work in regular Ubuntu, that for a user that installed the SteamOS session simply aren't working and are not going to work.
Example: https://askubuntu.com/questions/486879/return-to-unity-from-steamos-desktop-environment (note: I have the steamOS session on a Ubuntu 14.04 computer, and you can't logout normally...)
If it's not listed here, I wouldn't.
SteamOS is an application used with a custom Debian Wheezy release.
Questions about steamOS are off topic. Questions are better posted on their forums: http://steamcommunity.com/groups/steamuniverse/discussions/1/
As others have said, SteamOS is not an official Ubuntu derivative. Questions don't become on-topic here by being about SteamOS.
With that said, the usual guideline applies, that if the question is in some separate and significant way also about Ubuntu, it's probably on topic. For example, these questions would be on topic:
This isn't specific to SteamOS, nor is it related to whatever technical relationship (if any) exists between SteamOS and Ubuntu. This would be equally valid with SteamOS replaced by Fedora, Mint, Windows, or FreeBSD.
In general, when considering if a question that involves an unofficial derivative or other GNU/Linux distribution that's not listed here is on topic for Ask Ubuntu, consider if a similar question with an obviously less related OS, like Windows or iOS, in place of that derivative, would be on topic.