I didn't vote in the poll because I wasn't quite sure if it is referring to air or water temperature. If it is water temp, I know my limit, but it's not an option.
What stops me diving isn't the water temp, but actually the air temp. I've not had any problems with water temps above 40 degrees, and when we're down in the 41-44 degree range, I just require the air temp to be 65 or so, so I can warm up when I get out. The night dive I did a few weeks back hit my limit. Water temp was 39 and air was high 40's low 50's. That was just barely bearable for a 1/2 hour dive. My season ended last year not because of the 41 water, but because of the 41 degree air temp after the dive, when I couldn't just pop off my booties and warm my feet on the rocks.
I dive with a hood, gloves, booties, and a two-piece 7 mil suit.