To be fair, I have been stopped only once, about 8 years ago but if I were in their place and saw me walking down the street at the time, I would've stopped me. You can call it criminal profiling, II-profiling or what have you, but I am fairly certain that it was not racial profiling. Must have been my lousy choice of attire.
The experienced officers it seems have learned to tell the difference between those ethnic minorities who appear to be ordinary, law-abiding citizens/residents and those who match the visual profile of over-stayers/illegals. Further to this, I see ID checks being carried out on Chinese youth who fall within the age group described by Skyhook and, several times dodgy-looking mainlanders pulled aside for a check.