Dan is mostly correct, but...
When done properly, the misters can work really, really well. The trick is, the spray needs to be really fine so that the water will evaporate quickly. This evaporation will significantly reduce the air temperature. When this is working, you can walk under the misters and never get wet, and not get droplets all over your glasses.
I was in a park last season where a large number of misters were in use and they were all adjusted and working perfectly. What is so surprising about this story is that the park was Kentucky Kingdom, and the location was surrounding Swampwater Jack's, their big restaurant. Lots of cold-water mist, a couple of big fans running, but nothing was actually *wet*.
--Dave Althoff, Jr.