Former Alabama Congressman and gubernatorial candidate --and former Obama campaign chair-- Artur Davis is no longer a Democrat. At his blog he explains why:

parties change. As I told a reporter last week, this is not Bill
Clinton’s Democratic Party (and he knows that even if he can’t say it).
If you have read this blog, and taken the time to look for a theme in
the thousands of words (or free opposition research) contained in it,
you see the imperfect musings of a voter who describes growth as a
deeper problem than exaggerated inequality; who wants to radically
reform the way we educate our children; who despises identity politics
and the practice of speaking for groups and not one national interest;
who knows that our current course on entitlements will eventually break
our solvency and cause us to break promises to our most vulnerable—that
is, if we don’t start the hard work of fixing it.
On the specifics, I have regularly criticized an agenda that would
punish businesses and job creators with more taxes just as they are
trying to thrive again. I have taken issue with an administration that
has lapsed into a bloc by bloc appeal to group grievances when the
country is already too fractured: frankly, the symbolism of Barack Obama
winning has not given us the substance of a united country. You have
also seen me write that faith institutions should not be compelled to
violate their teachings because faith is a freedom, too. You’ve read
that in my view, the law can’t continue to favor one race over another
in offering hard-earned slots in colleges: America has changed, and we
are now diverse enough that we don’t need to accommodate a racial spoils
system. And you know from these pages that I still think the way we
have gone about mending the flaws in our healthcare system is the wrong
way—it goes further than we need and costs more than we can bear.
Taken together, these are hardly the enthusiasms of a Democrat circa
2012, and they wouldn’t be defensible in a Democratic primary. But they
are the thoughts and values of ten years of learning, and seeing things I
once thought were true fall into disarray. So, if I were to leave the
sidelines, it would be as a member of the Republican Party that is
fighting the drift in this country in a way that comes closest to my way
of thinking: wearing a Democratic label no longer matches what I know
about my country and its possibilities.

Also defecting, over same-sex marriage: Jo Ann Nardelli, Democratic Committeewoman, founder of the Blair County Federation of Democratic Women,Vice
President of the PA State Women’s Caucus, etc.

She said it started a few weeks ago, ironically as she and her husband
were getting ready for Mass and watching Meet the Press when Joe Biden, a
Catholic, cited his support for gay marriage.
This shocked her. She said she'd always related to Biden. She said he
reminded her of her father. But this announcement shocked her. And then,
shortly after, President Obama announced that he'd "evolved" into
supporting gay "marriage."
And then as a Democratic committeewoman she received her agenda from
the party espousing the same position. "To stand up and agree and sign
off on this I couldn’t do it," she said.