Lol where i live that would mean it gets used about 4 times a year!!dont ever ever ever take the air con off. the small weight it may save wont compensate on a hot day....trust me I have learnt this from experience.
unless your car is for track or drag use only I just wouldnt bother.
I've grown to not care about it, as chris said i'd rather jinx the weather by taking it off and have a great summer than not take it off and hope that we don't have another drab washout like this year has beenif it was cold, it may actually need a re gas????