For married Mormons: Where does OK end and sin begin?

It’s pretty clear that reproductive style “tab A in slot B” sex with your spouse (while thinking loving thoughts of your spouse) is OK, and waiting until your spouse is asleep and then sneaking into the computer room to masturbate to naughty pictures is a sin. But in fact there’s a whole lot of gray area between these two, and nobody seems to know quite where to draw the line. Of the following scenarios, which are sins? (No cheating by looking at the CHI online! )

Also — whether or not you believe in sin — which of the following actions do you think are or are not conducive to a healthy marriage, and why?

1. Bringing yourself to climax manually while thinking of your spouse is OK:
   1. never
   2. if your spouse is there participating
   3. if you’re away from your spouse for an extended period of time
   4. if you’re on the phone with your spouse
   5. if your spouse is busy, indisposed, or not in the mood
   6. whenever you’re in private.
2. What is OK to think about while having sex with your spouse?