Actually, that's not entirely accurate. What Congress passed was repeal of is known colloquially as DADT. The repeal also cedes to the Executive, discretion and time with respect to when the repeal is enacted. Then, like before the implementation of DADT, the homosexual military policy issue will be at the sole discretion of the President. He will, presumably, issue an Executive Order that will rescind the previous order of Reagan (I believe), and it's that order that will allow homosexual to serve "openly" in the Armed Services.
After Obama leaves office, the next President could (theoretically) reverse that military policy.
Of course, there is ongoing litigation seeking to prohibit (so-called) discrimination against gays serving openly in the military, which is wholly separate from this repeal.
DADT did not change military policy regarding homosexuals in the military, the prohibition on still existed in the military code of conduct.
This “repeal” will entail rewriting military codes of conduct to remove such prohibition and, among other things, extend some of the benefits to homosexuals that married couples have, a blatant violation of DOMA.