I appreciate all of the responses and the cautions that all of this is relatively subjective. I would, however, benefit from hearing some observations about drysuit usage by month in various places along the coast where some of you have extensive local knowledge, along the lines of: "At our surf sessions at Hampton Beach, NH, most paddlers are in drysuits until May, and resume wearing them in late September. Nobody wears them in July and August." (I made these observations up for the example...) A drysuit is a big $ investment, and at this point I simply don't have the data to decide if it makes sense to buy one, or to rent one for specific trips. I did find this table, listing monthly average sea surface temperature for a dozen locations in our region: http://www.nodc.noaa.gov/dsdt/cwtg/all_meanT.html