I don't have a percentage at the tip of my fingers, but I would say a significant portion of them have. These companies are independent businesses that are making the best decision with all of the options in front of them today.
In my experience in working with the entrepreneurs in Canada over the last 15 years, people have every intention of remaining headquartered in Canada, and they want to do business from here. What happens is that the reality of financing, funding and business opportunities forces them to make decisions that sometimes end up out of Canadian control.