This is a great question.
Fortunately, this topic has received considerable attention lately.
Notably, on July 25, 2007, the House Veterans Affairs Committee held a hearing on this topic, at which Veterans for America testified.
Veterans for America's prepared statement is here: http://veterans.house.gov/hearings/schedule110/july07/07-25-07/7-25-07forrester.shtml. Audio of the hearing and statements of all witnesses can be found on the right-hand column of this webpage: http://veterans.house.gov/hearings/index.html.
In addition, the Government Accountability Office (GAO), the investigative arm of Congress, recently announced that it will be conducting a thorough review of preexisting personality disorder dismissals.
One of Veterans for America's chief activities is ensuring that troops who have served in Iraq, Afghanistan, and elsewhere are treated fairly -- that their service is honored (for more information on Veterans for America work, visit www.veteransforamerica.org).
Veterans for America has been disheartened to learn from some service members, who clearly have service-connected mental health problems and/or traumatic brain injuries, that they were first diagnosed with a service-connected mental health problem such as PTSD only to later be told that they had a preexisting personality disorder.
While both the Army Regulation and the current Diagnostic and Statistical Manual of Mental Disorders (DSM-IV-TR) are very clear on what constitutes a Personality Disorder, the evidence that we've gathered indicates that, in some cases, this diagnosis is being arrived at hastily. In addition, some in the military health care system appear to be attempting to defend the broken practices of the past. Fortunately, other military leaders have clearly stated to Veterans for America that they know that problems such as poor mental health treatment has existed and that the military is working to do a better job of honoring our commitment to those who have served our country in the military.
For more regarding Veterans for America's stance on what we owe those who have served in our military, I have provided a link to an essay by Bobby Muller, President of Veterans for America, entitled "What does America owe to those who serve?" -- http://www.veteransforamerica.org/index.cfm/page/weblog/subpage/display_blog/bid/486CA50C-123F-747A-1B0769A57C558D42