I have my own carnival (Personal Stories of Change
) and also regularly submit to other carnivals.
Blog carnivals have helped me to establish an online profile and also to break the ice with a number of other self improvement bloggers (who I have since gone on to become friends with). Also, they provide links to my articles which is good for SEO. In terms of traffic, though, I notice very little (if any) extra traffic directly related to blog carnivals.
Hope that helps