some questions clearly belong to more than one site
That may be, but you should ONLY post a question where it BEST belongs. If the question applies equally to all three sites, then you must decide what kind of answers do you want:
- Do you want someone to come up with a scripted/programmed solution? Go to SO.
- Do you want someone to tell you how your problem may be solved through server configuration? Go to SF.
- Do you want to know how it may be solved using off the shelf programs? Go to SU.
If you have NO idea in which field your problem may best be solved, then post it on SO, and let the programmers there vote it to the place where they believe it has the best chance of being solved.
If you want to explore all three options, REPHRASE THE QUESTION SIGNIFICANTLY so that it's CLEARLY different than the others and SPECIFICALLY calls for a programming, server configuration, or COTS solution.
If it's not blindingly clear to everyone that the question belongs on the site it's asked on, it will be migrated, and if you've asked the same thing on the other site one or both will be closed as duplicate.
Asking good questions is an art that requires effort BEFORE you hit the "Ask a Question" button.