2. Obviously people do get drugged occasionally, the inventor seems to have had it happen to him
3. Unfortunately there seems to be no real evidence that GHB or ketamine are often used in sexual assaults, and even Rohypnol which has the worst reputation has not often been detected. A straw that could detect a drink that's stronger than you think it is might be more useful, AFAICT the number one date-rape drug is alcohol.
(I want to be absolutely clear here, I'm not saying date rape doesn't happen, I'm not saying that some really nasty people don't deliberately get others into pliable states to take advantage of them, but AFAICT the use of drugs in the way the media likes to run scare stories about is very uncommon)