I have a question about wiring up an ethernet face plate and I'm unsure whether I should ask here, StackOverflow or SuperUser.
Should I ask on multiple sites or just the one specfic site?
I would say wiring questions are a better fit here. Once you start connecting and configuring devices I'd take any problems to SuperUser.
We already have some good questions here under data-wiring:
I think asking about what type of wire to run, how many to run, etc is a better question for SuperUser, as that stuff is ultimately dependant on what you want to do and what equipment is being connected.
Asking about how to physically run the wire is better suited to DIY. Examples off the top of my head would be questions involving: conduit, code compliance, "can I drill through this beam?", fire ratings, fishing, running through an exterior wall, enclosures/junction boxes, etc.
There is going to naturally be some grey areas, such as running phone with cat3 vs cat5e/6, or if it makes sense to use a long HDMI cable vs HDMI-over-cat6 adapters, and I think the best way to deal with that is to answer at least from the DIY-related aspects (eg, "running a long HDMI requires bigger holes to be drilled, since you can't crimp the ends like you can with Cat6.") and defer non-related parts to superuser (eg, video quality of one vs the other).