i think if you ride around the city it would be a very good idea to have them. being seen is very important. there have been numerous amounts of times when i've driven down the road, and saying to myself, "gee, if they didn't have reflectors i wouldn't have even seen them."
reflectors are not even that great. sometimes when driving at the wrong angle, i can hardly see them on someone's bike. if you're going to ride at night, put a front and rear light on please, for driver's sake if not yours.