Minxi and I recently got invited to join Hong Kong Stuff:
Hong Kong stuff is a fun, not stuffy social website by and for expats living in Hong Kong. It's format is very open and friendly. Everyone has their own blog and the main occupation seems to be to post pictures of your latest adventure in Hong Kong. They are more the local crowd than the hotel crowd but they probably know where the good guesthouses are.
The site is divided into what part of Hong Kong you are living in. My invite came from someone in the New Territories. Some of the groups seem to be very active taking their socialization off the internet and into the real world in the form of dinners, Hiking events and the like.
Minxi and I are members (see our flair below) but we can't really do much at the moment because she's still in China and I'm back in Topeka. If you're interested in Hong Kong and expat life, or if you are an expat in Hong Kong, I strongly suggest you try out HKS. They're a great bunch of folks and I'm sure they'd love to have you on board.
Good luck exploring Hong Kong.