Re: Person of Steel, Significant Other of Tissue paper
In DnD i had my DM once flat out ask me if my character and his cohort were having sex together. I told him that he'd have to ask them and i didn't know.
As far as in other, more serious games, I've seen someone pick up a GF in a "red sonja" way. It was funny because she was actually built on more points than us, kori just happend to be the second one to fight her and so he got to knock her out, after she beat down pedric.
I've been in a sci fi game where a psyic cat girl went into estrus and got pregnate and the GM wouldn't tell us which of the 6 possible fathers were actually fathers, plus how many babies there were. That was good times.
Finally i've run a game loosely called "Soap quest" where sex and relationships are treated lightly and mostly just used for comedy.