The involvement of the person behind the project is really important. Submitting bugs and patches is one thing, but if none one looks at them, why bother? In fact it's a two way route: the more involved the original developer, the more people will take interest in the project.
I submitted bugreports on several occasions in various projects. Most rewarding was when I submitted a small bug in Magpie. I got a personal reply by mail from the original developer. Seeing how your solutions are considered by the developer and how your contributions matter is big aspect of what's open source all about.