I have two models with a HABTM relationsip: users & interests… Basically the purpose of this is that when a user is registering they will be able to select interests.. Anyways, i have the forms setup and working (saving to the DB) but am not sure if it is the “proper way”.. See screenshot of DB data.. For example, the last test user i created (user 7) had selected many interests.. should these be saved as an array or is this OK?

It is the normal way. It creates one row per person/interest pair.