I just bought the non-breathable version yesterday from a local store. I wore it in to work today, and I'm praying that the LBS will take it back. It's like having my own personal sauna along for the ride. It was about 50 degrees out this morning. I think that this jacket would be okay for sub 40 degree riding.

I'm going to pay about $20 more and get a nice water resistant wind breaker from REI. It's even got removable sleeves. That will keep me dryer and more comfortable than the $50 rain jacket.