I'd love to see the percentage of Unity games that were not completed in time vs. C2.
imho - if you are attending a gamejam.. you need to use a tool like C2... it's perfectly built for a jam.. I think Unity is a little overkill.
I ran a GGJ site here in my town - I didn't participate (since there's no time while organizing and running the event) but I helped out a lot of people all who were using Unity. I kept thinking, "I could do that in 2 seconds in C2".