I have a dormant Shelfari account that I won't migrate. I am not dedicated to the cause of maintaining records of my reading. I tend to graze the reading landscape rather than create lists of expectations. I read what I like in the moment and never like to be held to account when I change my mind.
GoodReads will allow you to migrate your Shelfari account. The instructions seem overly simplified for something that I expect will take more steps. You can search the Internet for other instructions. I would take some of them with a grin of salt. If you are panicking, do some research before you press any buttons.