Fish, its a valid feeling in that it is very very common and there are often deep seated, subconscious reasons for it, often stemming from the persons childhood. Most people recognise they shouldnt feel this way and they come to terms with it and love their baby just the same once its here. Theres a huge difference between a bit of disappointment upon finding out a sex but shortly getting over it, to aborting or even killing the baby when its born because of the sex. I would say that the situation in China etc isn't even 'gender disappointment', its about a deep cultural belief that women are worth less than men, a society that doesn't value women at all, which is common in many Asian countries. In China perpetuated massively by the one child policy.
I have to say theres some right twats on that ingender website if anyones seen it, one main poster who had 7 DDs before finally having a DS, only ever wanted 2 DS in the first place, finally had her DS conceiving him just after she had her last DD. She openly stated that the age gap was way too small and stated that she was breastfeeding her DS and her youngest DD fell on the floor or something and was crying and screaming out 'mama!' for her, and she stated she just sat there and did nothing because her beloved DS was latched on and she didn't want to move him. She then stated she didnt have time to 'baby' the youngest DD because of the DS arrival, So basically neglected her youngest DDs needs who she only had in a quest for a DS. I felt sick upon reading that post, and whats worse is she got no criticism whatsoever! An attitude such as that is definately wrong, particularly having lots of children whose needs you then neglect because you have yet more children to look after due to your quest for a certain sex. So yes, whilst I acknowledge its normal for people to be disappointed at first, I draw the line at this type of behaviour, having DC after DC and not providing what they really need, all so you can have a certain sex.
I've never had a case of 'gender disappointment' myself, by the way.