from The New Birth Order Book, written by Dr. Kevin Leman:

the middle child is...
1. more of a closed book than an open one
:secretive, plays "closer to the vest" relationships. [harh?]
2. likely to be mentally tough and independent
3. teenage middle children often run with the pack
:hang with the crowd...
4. likely to be the most faithful marriage partner [O.o?!]
:compared with other birth order [ie first borns/ last borns, etc.]
5. probably embarrassed easily
:but would never admit it. [DURH.]

typical traits:
-grew up feeling squeezed and rootless
-reasonable expectations to life
-social lion
-independent thinker
-compromising
-diplomatic
-secretive