Actually, there is some truth to this!!
Male sperm (the Y chromosome) are faster but weaker sperm; they will arrive at the uterus more quickly but also die off faster. Female sperm (the X chromosome) are slower, but stronger; they arrive later and stick around longer. Therefore, in theory, if you have sex on the day you ovulate or immediately afterward, you are more likely to conceive a boy because the male sperm will arrive at the uterus first and fertilize the already waiting egg. However, if you have sex in the day or so before you ovulate, you are more likely to conceive a girl, because the male sperm will arrive first and die off because there is no egg to fertilize, while the female sperm take a little longer to arrive and are strong enough to wait around a bit for the egg to finally enter the uterus.
This is not 100% fool-proof by any means, but it does have some scientific backing! Good luck TTC!
at 11:19 AM on Oct. 8, 2009