I wore a Snowsled Ventile smock in awful Scottish weather last year and was very surprised at the performance. The key, I think, is to wear the right stuff under it. With a Marmot DriClime top as my base layer I found that the tiny amount of water seeping through never seemed to reach my skin, and I was always warm and comfy. I habitually wear the smock when hiking, but also every day for the journey to work. Well, it wasn't cheap and I like to get a return on my investment...
The relatively slow drying times of Ventile have been improved by new proofing treatments like Grangers and Nikwax, and I think I'd only worry about that for very cold and wet conditions. Since it's so versatile and comfortable I also found that I carried less clothes, offsetting the slightly higher weight of the cotton when compared to synthetics. I do own other waterproofs, including a very experienced Paramo jacket and a Buffalo Mountain Shirt, but the Ventile smock is the one I reach for most of the time these days.