civil_servant: For a roach, I think you'd be looking at more like $500 and a few hours at a police station before going on your merry way. Maybe even just a caution if you're lucky. That would be for the first time. You could be looking at a larger fine and possibly even a week in jail the second time.
I've declared excess alcohol at the airport before (twice). They were very surprised at my honesty and that I speak some Cantonese and said they'd work with me to charge me the least they could. They were very friendly both times and made lots of small talk. Worked out to HK$40 a liter or so. Much easier than having to deal with fines and things