Gabriel Arana has an article on DADT:
Gay and lesbian study participants who were asked to conceal their sexual orientation performed 20% worse on spatial reasoning tests and 50% worse on physical endurance tests as compared to those who were not given this instruction. The findings have clear implications for the battlefield. Gays and lesbians even those who follow the policy are prevented from performing optimally, which may affect the readiness of military units.
Bonus blog post here.