Sorry can't help with the SIDS mattress question, very interested in the answer though! Surely it would apply to parents using the mattress for a 2nd DC, not just if you give the mattress to new parents? I'm just speculating, I have no idea.
As for the gender selection thing, ALL parents have "incorrect" habits/opinions/preferences about something. I imagine most parents screw up their kids a little, isn't that part of the job description? Why is gender selection worse than a family that chooses to have more children than they can afford? Or families that insist on specific roles for girls vs boys (even though they're equally loved) personally I find them to be far more worrying than a person who is just apprehensive about knowing how to parent a boy. The people I know who prefer a particular gender it's not normally because they hate the other gender, it's usually just fear of the unknown, or wanting to experience parenting both. I don't think they should be vilified for that.
As for the population balance, there are numerous countries where gender selection is legal, including the US, and in all cases the percentage of people actually going for it is so low that it's had no impact on the population ratio.
I hope I'm not coming across as dismissive of anyone else's view. I respect and understand why you would have concerns about a person who is completely unwilling to love a child of the "wrong" gender. I'm just expressing my personal views on the matter, and not trying to browbeat anyone into agreeing.
Now someone mentioned we have an exciting week coming up! Apart from the imminent pain-free arrival of Ninja's DD (yay!) what else is on its way? Sorry, would someone mind summarising for me please?