Got caught in a driving rain in 50 degrees (F) for over an hour and my Gabba kept me warm and dry. Fabric can get a little clammy next to the skin on its own, so I usually wear at least a light mesh base layer under it, which gets rid of that problem. I find it breathable enough for most situations, and of course it's got a full length zipper for regulating temps. It's definitely more wind resistant than a conventional cloth jersey, and that's a real plus, but not totally windproof like full Gortex, That's Okay because it lets it breath. On really windy, cold days, I use a Craft base layer with windstopper on the chest for additional wind protection underneath. Its great having a jersey like this on when you leave home and there's a chance of rain. Don't have to pack a full rain jacket just in case and the Gabba is more streamlined and doesn't billow about.
I have used it regularly this Fall/Winter here in Colorado in temps down to the high thirties with arm warmers and a good base layer. Unless you know you are going to be riding on a rainy day, this is not a warm weather summer jersey. This is more of a three season Fall Winter Spring classics type for temps below about 60 degrees F. Rear pockets are very deep, which is great for storing additional layers on transitional days. Sleeves are longer than usually found on a short sleeve jersey, which means there's no gap between the top of your arm warmers and the jersey sleeve on cool days. The extended flap on the back is great for keeping your butt dry in wet or slushy conditions.