It's pretty big.
I'm about as military as a chocolate truffle. I have no interest in weapons and very little interest in military ritual and protocols. Clausewitz said that war is an extension of politics. I think war is a failure of politics, and that there are only 2 kinds of wars, desperate necessity and gratuitous aggression.
The repeal of DADT will have big consequences for gays and lesbians beyond the military. Acceptance of gays and lesbians into the military will make the case against granting them legal equality much harder if not impossible. The depravity and pathology arguments will be dealt a huge, if not fatal, blow. If gays aren't too sick and twisted for the military, then they're not too sick and twisted for protection against housing and employment discrimination. Those of us who live in big city relatively gay-friendly enclaves forget that it's still legal to deny people housing and employment on the basis of sexual orientation in most of the country. The case for gay marriage will be strengthened that much more by this.
This may well have an impact on religious arguments over the status of gays and lesbians. The depravity and pathology arguments will be harder and harder to make as gays and lesbians enlist and serve openly in the military. The religious defenders of homophobia will be forced back to ever more literal interpretations of the handful of Scriptural passages that condone it. This leads to the complication that if these passages are still binding, then what about other more exotic and quaint legal regulations in Leviticus and Deuteronomy?
Since this is a big transformation, expect a big backlash, especially from the new Republican Congress next year. I think the Republican leadership wants to get rid of the gay issue. It was a winner for them in the past, but now, it's become an albatross for them. Expect a lot of extreme rhetoric from the party's fringes and maybe a violent incident or two.
White middle class America has decided to accept its gay children (middle class minority America is more complicated and still evolving on this issue). I think both right and left want to move forward to other issues.