Hey Sean,

I am sorry that delay of this reply,

Basically when the new user come to register via Easysocial registration page is actually same as register in Joomla, just that Easysocial like a layer can extend extra special custom fields for user details. If the user register in Easysocial, the process will add the user into Joomla as well.

Regarding with your free membership question :
It actually depend on how do you configure with your Easyblog ACL and Easysocial profile type (inside Joomla user group).
Example :
Easyblog ACL
If you set Easyblog > ACL > Registered user group > publish/write entry - NO
- which mean that which user under "Registered" user group, they will not have permission to write and publish post in your site.

If you set Easyblog > ACL > Gold member user group (example) > publish/write entry - YES
which mean that which user under "Gold member" user group, they will have permission to write and publish post in your site.

Easysocial Profile type user group
Let say you have created 2 profile type :
Free Membership group - Assigned to Joomla Registered user group
- Under this profile type, user do not have permission to write and publish post in your site.

Premium Membership group - Assigned to Joomla Gold member user group
- Under this profile type, user have permission to write and publish post in your site.

Hope this will helps.