Good but bad Rated 2 out of 5 stars
I like Stumbleupon. I really do. It has helped me find many great sites. I just have one problem. They will not allow you to remove an email address from their system once it is there.
So if you care if someone else has access to every email address you have ever sent to then for the love of God do not import them because you will never get them back out and deleted from their system.