The Economist writes about a study that looked at business improvement districts -- groups where businesses band together to hire security guards, litter patrols, etc. They're essentially the same as the Community Improvement District that operates downtown, i.e. the people who hire the guys dressed like bumblebees. The average benefit-to-cost ratio is about 20 to 1 -- for every $10K spent, they get about $200,000 worth of crime prevention.
It's not crimefighting in the traditional sense, but keeping the streets clean, helping visitors and simply having eyes posted -- stuff that regular cops don't have the time to do -- can play a big part in crime prevention, it appears.