Your mom, neighbor, plumber, kids' teachers are probably people who's name, birthday, phone number and email address you probably want to remember.
GoldMine already tracks your professional contacts, why not keep all your contacts in one place? There's no reason not to, except you don't really want other people at your office seeing those names and numbers. You don't really want that weird Joe guy sitting next to you dialing up your sister thinking she's a prospect!
To keep a record, any record, in GoldMine private to you we set it's ownership and curtaining. Ownership determines who is the owner of the record. A record that is owned cannot edited by anyone other than the owner of the record or someone with master rights. Curtaining determines how much of a record (if anything) a non-owner can see.
When these options are set they’ll be set for the contact record currently being viewed. To set Ownership and Curtaining we go to Edit | Record Properties | Record Related Settings.

Then choose the Ownership tab.
Set “Owned By” to the user or user group who should own the record. Then set Record Curtaining to the appropriate level.

If curtaining is set at None the entire record will be visible. If Semi-partial is selected the top half is visible but none of the information in the tabs. If Partial is selected then only the top few lines of the record (Name and phone numbers) are visible. If Complete is selected then the record will not appear in the search center or anywhere else. Complete would probably be the appropriate setting for contacts of a personal nature.