(Note: I'm a UL mod, so when I say "we" I mean Unix and Linux Stack Exchange)
If it's a question about Unix and Linux and you don't want it, odds are we do; we're fairly inclusive. We have this same overlap problem with other sites, notably Ask Ubuntu, so here's what we do with them:
- Questions about Ubuntu that have no bearing on other distros are migrated from UL to AU
- Questions about Unix or Linux that don't apply to Ubuntu at all are migrated from AU to UL
- All other questions are left where they're posted unless the OP asks us to move them
I generally apply the same logic to other sites, even if we haven't specifically talked about it. So we almost never migrate here (3 times in the last 3 months), because it's rare for someone to ask a sysadmin question that doesn't involve Unix or Linux. Similarly, we don't expect you to migrate Unix/Linux questions to us if they're on-topic here -- you should only migrate a question if SF isn't a good place for it, or the OP changes their mind and wants it somewhere else.
I'll also mention that one thing you shouldn't do (or encourage others to do) is cross-post. Sites differ on their tolerance for cross-posting; we usually close a question if we find out it was posted on multiple sites. Either pick a site, or tailor your question for the individual sites you're asking it on -- don't just copy/paste it to all the sites that sound relevant
