Man... if it was 70 here, I'd definitely be out on the water!
I usually try to get out there anytime it's above 60; and it's been touching 60 here this week. Unfortunately the boat's dismantled and stowed for the winter.
For 70, I'd take the day off and go for it!
Down here I am permanently annoyed with most of my friends during the winter months, I seem to be the only south Texan who doesn't hibernate when the temps drop below 75. Every weekend its the same story:
"Hey, wanna go Kayaking/fishing/sailing/combo there of?"
"Your nutts, its cold"