I suck at mongoid

1_user.rb

class User
  include Mongoid::Document
  references_one :best_friend, :class_name => "Person"
  references_one :worst_enemy, :class_name => "Person"
end

2_person.rb

class Person
  include Mongoid::Document
end

3_i_fail.rb

person = Person.create!
user = User.create! :best_friend => person
user.best_friend  # => #<Person _id: 4d781dbd568ab57112000002, _type: nil, _id: BSON::ObjectId('4d781dbd568ab57112000002')>
user.reload
user.best_friend # => nil

Double-check that the record hasn't been created by going through the mongo shell. MongoMapper tends to not behave well in the console, Mongoid might be the same. Other than that, it looks right.

they're being created, just not being linked. Guess I need to spend more time reading the mongoid docs to figure out references

Your Person model is missing the inverse reference.
class Person
include Mongoid::Document
referenced_in :user
end

I'm not sure how the custom naming will fit in, though.