Taxonomy is the formal, hierarchical structure of tags which are usually managed by staff. Folksonomy is similar to taxonomy, but users create the tags. Members, Volunteers, Donors, Board Members, Chapter Leaders, Registered Users, or anyone you allow can add tags to your folksonomy. SharePoint offers both, and both are very important.
In SharePoint 2010, Terms are your taxonomy, and Keywords are your folksonomy.
Personalization can also be achieved using SharePoint Audiences. Audiences are logical groups of users that you define with similar attributes.