Polling programs

I've played around a bit with Survey Monkey and Poll Daddy, but probably not enough to know the answer to my wn question. Since I'm a strong believer in the power of collective wisdom, I will consult you! Someone in my state tossed out today that our annual book award nominations may use a program like these for kids statewide to submit their vote. Is that feasible? Can these sites be set up to allow voting only one time per student? What is to keep students (or maybe teachers) from voting in multiple grade bands' elections? I guess what I'm asking is can these be set up so that a person or group cannot skew the results?