i'm there now on secondment for work, depends where you are staying the runing is both spectacular and infuriating.
it is hot, humid and hilly, you have to be up early to avoid the humidity and Central is packed with people. But get out of the city onto the long distance trails and it is astonishingly good. Places to run include the HK trail and Bowen Road, also look up AVOHK a very good group of runners, i've run with them for a few weeks, weekly time trial on a saturday, long run on a sunday and track sessions on tuesday and thursday nights.
the track sessions often take place in 30 degrees and 90% humidity, it all takes a bit of getting used to, but the extra effort makes the rewards greater.
Let me know if you need any further info
john