Personal companions crowd-source and/or crowd-share characterizations, and optionally raw data, from real-world, virtual and/or mixed-reality experiences. Characterizations can advantageously be stored in one or more self-evolving, structured databases, and can be organized according to objects, actions, events and thoughts. Characterizations can be weighted differently for different users, and “forgotten” over time, especially in favor of maintaining higher level characterizations. Personal companions can be used to obtain additional information, and conduct interpersonal, commercial, or other interactions or transactions.