Interesting discussion.  I came to the solo canoe after years of whitewater and touring kayaks.  While I wanted to learn the single blade, I was very nervous about having just a single on my first trip.  I used the double blade for about an hour, put it away, and never looked back - I find the single blade much drier, quieter, lighter, and every bit as efficient.  

My knees tell me I'm too old to convert my whitewater kayak to a C1, but I'm toying with building a short canoe paddle to combine with the K1 on the local river.