The short answer is no. I've never worn a wetsuit sailing in cold weather, but I've been scuba diving lots in all kinds of weather. I live in Canada and have dove here in every month.
Wetsuits are for keeping warm under water. On the surface, water will evaporate from the neoprene and chill you. For example, between dives it's better to strip out of the wetsuit and get into something dry to stay warm.
The other thing is mobility. We use mostly 6mm suits which are restrictive. This might not be as much of an issue with thinner neoprene, but still applies.
While this thread is 4 years old, the advice is still sound. The best bottom layer is synthetic microfibre, like polar fleece. Avoid cotton altogether.
Last edited by CapnHand; 09-30-2007 at 03:07 PM.