Depending on when you get there, you may want to check out Repulse Bay (http://en.wikipedia.org/wiki/Repulse_Bay) or one of the night markets. (Needless to say, that would require you being there in the evening. Spending an afternoon layover at a deserted night market would probably be rather boring.)

The city is pretty exciting (lots of small stores and parks to perus), and the public transportation is pretty good as well. Don’t let the computer terminals in the subway intimidate you: you simply have to select your origin and destination beforehand, and then you’re charged by distance. (What a novel concept!)

Have fun!