Yes they do say that if you only BD several days before ovulation then you have a higher chance of conceiving a girl as the 'girl' sperms are slower but can live longer than the 'boy' sperm.
I also heard that if you are eating less then you are perhaps more likely to have a girl, something to do with the egg being selective over which sperm it allows to penetrate - some remnant of when times were hard and more females born would result in more future births. Though I think this theory is to be taken with a pinch of salt.
It's interesting though, that when I conceived my daughter we BDed 4 days before I usually ovulate (I cannot confirm on which CD I ovulated on that cycle though)
and also I was on a pretty stupidily restrictive diet back then.
I also read that female sperm favour a more acidic environment. But that seems a bit daft to me because I also read that an acidic environment will kill all the sperm. There's a lot of conflicting info out there, but there are some theories about eating different foods which will alter the PH of the vagina making conceiving a particular gender more likely.