I’ve just installed my MyBook Live and registered with MioNet. On the MioNet website it shows a monthly or annual charge. I was under the impression from the WD site that usage of MioNet was free with all WD network devices.
Based in the user manual of the WD My Book Life, your account of Mionet is free, it looks like you create an account in Mionet site and then, using the drive interface, you register the drive and linked with the Mionet account.
The basic version that only allows you to see your drive is for free. To be able to access your Desktop, your My Documents, all drives connected to your computer, and the video capability will cost the extra monthly charge.