Excellent topic - I will do my best to answer this as a western guy who married an Chinese Australian Woman.
1. is it true or a myth that local girls fancy western guys? My wife did, but I am really attractive so it wasnt hard . In all seriousness, locals not so much (unless they were educated abroad), but the Canadian, Australian, UK/US chinese women tend to me more accepting and willing to date western guys. They usually will socialise with them also.
Some people confuse filipinos with local women. You will find THOUSANDS of filipinos (often under 30) married to old balding white guys (over 60).
2. heaps of western women find it hard to get a date (myth or reality?)
Yes and No - Easy to get a date, but the single man scene here can mean if you have half decent looks, you can pick up and screw around all you want. Long term relationships are hard by all women. There are alot of cheating going on. As one poster mentioned, some people come for fun, then go home back to their partners.
3. most girls in HK are shallow, and finding a marriage partner is hard (myth? reality?)
Yes, many of my local female friends are always pestering me to set them up with men I know. I feel scared for the men, they practically throw themselves on them. I think after 33+ women generally start worry about babies more and want to settle down. Woman are super successful here and career takes first place in their 20s. Once they are established, finding a partner takes centre stage. Shallow... no all women (and men) want a quality partner. Some demand more.
4. are there single women there from other ethnic groups there too? Indians, for example?
Everyone is in Hong Kong. Unfortunately too many french. =P
5. for men, would you say it's rather hard or easy to meet women?
Easy to meet women. I would say the easiest place on the planet to meet women.
6. for women, what do you think of the men in HK (both local and expat).
Can't answer that as a guy. My wife says that she had to come to Australia to get me cause the quality in HK was so poor. She has had 3 other friends who now have moved to Sydney where they have found great partners, but each of them complained constantly to her that HK had no nice men.
You know the rule - Good ones are married or gay. True in Hong Kong.