Rarely will I give a beggar anything. I'm pretty sure I know what they are after with their money. There has been two seperate occasions where I've seen people begging for change talking on cell phones. If you are doing something, like playing an instrument, I will throw some money your way. Then again, that is not begging. That is working as a street performer.
Maybe I sound cruel here but I'm not about to support someone's drug or alcohol addiction.