Well...our water is still liquid - went sailing yesterday on a 29'er (it was my first time and very likely my last). Air was 60 and the water was about 48-50. One forestay strawberry on my forehead and three capsizes later I discovered that my dry suit is leaking. I was chilly.

But to answer your question, 70 degree water is hard to consider chilly but we did have a big cold front come through a couple of years ago for Tradewinds that caused a minor stampede at West Marine for foul weather gear. The rest of the times a pair of shorts and a spray top was all that was required.