It depends. I've dropped my pledges after seeing updates that showed me the project wasn't what I initially thought (which was the case with Massive Darkness 2), but sometimes they put me over the fence to back when I liked what I saw (which was the case with Savage Pathfinder).
So I think in either case, if you get more pledges or cancellations, it's a positive in that your backers are making more informed decisions and are less likely to be disappointed in the product.
So I think in either case, if you get more pledges or cancellations, it's a positive in that your backers are making more informed decisions and are less likely to be disappointed in the product.