Cool app! IBM is in the process of significantly updating their documentation on User Modeling, but meanwhile, here are some basic descriptions of some of the traits, as well as links to some of the research behind the service.

User Modeling analytics are developed based on the psychology of language in
combination with data analytics algorithms. User Modeling extracts three types of
personal characteristics from the data a person generates in social media or within
their written/digital communications:
Big 5 Personality - This is the most used personality model that generally
describes how a person engages with the world by the following five
dimensions:
– Openness-to-Experience - associated with curiosity, intellect, and an
appreciation for art and adventure
– Conscientiousness - associated with organization and industriousness
– Extraversion - associated with positive and outgoing attitudes toward other
people
– Agreeableness - associated with compassion and cooperation toward other
people
– Neuroticism - associated with a sensitivity to negative emotions
Each of the five top-level dimensions has six sub-facets that further characterize
an individual at a finer-grained level.
Basic Human Values - this model describes motivating factors that influence a
person's decision-making. Our current model includes five dimensions of human
values based on Schwartz's work in psychology:
– Self-Transcendence - motivated by helping others
– Self-Enhancement - motivated by increasing social status
– Hedonism - motivated by pleasurable experiences
– Openness-to-Change - motivated by experiencing new things in the world
– Conservation - motivated by tradition and conformity
Fundamental Human Needs - this model is based on Maslow's hierarchy of
needs and Ford's work on Marketing and consumer-related needs modeling. It
describes, at a high level, which aspects of a product will resonate most with a
person.
– Ideal - the person likes high-end, finely crafted products
– Self-Expression - the person likes products that express their individual
identity
– Closeness - the person likes products that help them establish closer
relationships with family and friends
– Excitement - the person likes products that provide exciting, adventurous
experience
– Practicality - the person likes products that simply get the job done

For more detailed information about the research and technical background behind
the User Modeling service, see the following:
You read what you value: understanding personal values and reading interests
Gary Hsieh, Jilin Chen, Jalal Mahmud, Jeffrey Nichols; CHI 2014. 983-986.
Understanding individuals' personal values from social media word use Jilin
Chen, Gary Hsieh, Jalal Mahmud, Jeffrey Nichols; CSCW 2014. 405-414
Recommending targeted strangers from whom to solicit information on social
media
Jalal Mahmud, Michelle X. Zhou, Nimrod Megiddo, Jeffrey Nichols,
Clemens Drews; IUI 2013: 37-48
Modeling User Attitude toward Controversial Topics in Online Social Media
Huiji Gao, Jalal Mahmud, Jilin Chen, Jeffrey Nichols, Michelle Zhou; ICWSM
2014.
Who will retweet this?: Automatically Identifying and Engaging Strangers on
Twitter to Spread Information Kyumin Lee, Jalal Mahmud, Jilin Chen, Michelle
Zhou, Jeffrey Nichols; IUI 2014. 247-256
KnowMe and ShareMe: understanding automatically discovered personality
traits from social media and user sharing preferences Liang Gou, Michelle Zhou,
Huahai Yang; CHI 2014.
Identifying User Needs from Social Media Huahai Yang, Yanyuo Li; IBM
Research Report.
PersonalityViz: a visualization tool to analyze people's personality with social
media Liang Gou, Jalal Mahmud, Eben M. Haber, Michelle X. Zhou; IUI
Companion 2013: 45-46