Recently, the Journal of Social Issues (JSI) published a study that found that multiracial people who identify with multiple racial/ethnic groups tend to have a greater psychological well-being and social engagement than multiracial people who identify with one group:
Multiracial Identity Associated With Better Social And Personal Well-Being
ScienceDaily
http://www.sciencedaily.com/releases/2009/02/090210110045.htm
(NOTE: At the bottom of the ScienceDaily article, under Journal reference, you'll find a link to the actual JSI study.)