"Don't Ask, Don't Tell" was never a good policy. There is no evidence that sexual orientation has any bearing on the ability or willingness of men and women to serve as soldiers or to perform their duties as ordered and required. The only impact has been to deny highly qualified individuals the opportunity to serve, and deprive the military of their services.
The argument that sexual orientation will disrupt unit cohesion has largely been put to rest, both by the study of unit cohesion in militaries that do not discriminate against gays and lesbians (Britain, the Netherlands, and Israel, for example; 20 of NATO's 26 member countries allow open gays and lesbians to serve in the military), and by the increasing flow of anecdotal evidence from American soldiers serving in Iraq and Afghanistan.
The banner of resistance to this acknowledgment of change is at least two generations behind the time: as the brother of an openly gay teacher and the father of two sons, I can see that the next generation considers this entire issue irrelevant to the quality, capabilities, talent, and companionship of young people in their generation. I am tempted to say: "Get over it!"
And to those who argue that this is "social experimentation" in the military...please....!! Where else have we done so much to further change in our society? Perhaps this is the one institution where justice can truly be served. Racial and ethnic integration happened here, earlier than in America's schools. The only truly national health program in this backward country is in the military and, yes, it costs money - $50 billion this coming year alone. One of the best retirement systems in the country is provided the men and women of the military; would that the entire country had the same benefit. Some of the "best practices" in family and mental health support, in prosthetic treatment, in family housing, happen in the military. DOD funds some of the most thorough AIDS research in the country. The military is a "command" system that can carry out such changes, often ahead of the rest of America.
The supporters of "Don't' Ask, Don't Tell" have been funding all that "social experimentation" and change for decades, even demanding that it happen. So it is truly time to put this one to rest and get on with the job.