Agreed with JGL
I too am an overseas Chinese and my Cantonese sucks as growing up I was taught Hakka which was a common language amongst people in the New Territories.
I haven't found it a hindrance at all not being fluent in Cantonese and also not able to read or write it. All it does is restrict the places you can apply for work but then I wouldn't want to work for a 'local' company anyway due to the office politics and the back stabbing and staying late just so your boss can notice it and that crap.
I came over here from London and it took me all of ummm 4 months or so to feel properly settled out here and in a working routine alongside an active social life through lots of wonderful people I've met through here
HK can be seen as shallow and status oriented at times but you soon get used to it and after a while its water off a ducks back.
So don't worry about it and come over whilst you're still young and have fun out here, Thats what I'm doing and don't plan on going back to U.K anytime soon.