The saying, "This ain't your father's Republican Party," can likely now be extended to the Democratic Party as well.
Arguably, the election of the first not-White President has done a lot to visibly shake up the right (especially the authoritarian right), and the massive recession and perceived slow recovery also shook up people all over the spectrum. It's inevitable that left-wing politics (associated primarily with the Democratic Party) is being shaken up as a result (with one of the major changes being an increase in the vocality of an "authoritarian left").
I think that there were a number of social issues that have reached "tipping points" during the period leading up to Obama's election, including LGBT rights, legalization of marijuana, gun regulation, global warming, changes in religious affiliation, and the role of religion in politics. Although I have no evidence for this, I do believe that the election of a POTUS perceived to mark the transition of an era in the country gave so many groups an impetus to push their cause over that stalled tipping point. (And although not definitive evidence, a lot of social polling seem to show that a number of these social issues started to move since 2008; some showing increased oscillation, others showing opposition, and still others showing acceleration.)
As a president who continues to be touted by the left and the right as a symbol of the US' capacity to change (whether that change is seen as "good" or not), I think that POTUS' public endorsement (or lack of one) on a number of social issues only helped speed some issues beyond their tipping points while stalling others. For example, his endorsement of SSM only accelerated the public perception in favor of the issue, and his lack of endorsement of clear cuts to carbon emissions has stalled that debate.
I would say that when people look back on the Obama years, it will be to note how quickly so many social norms just gave way after decades of stalling. Of course, the determination of whether this was a "good" or "bad" thing for the nation can only be made in hindsight.
It is undoubtedly true that (a) these past six years have witnessed major shifts in the socio-political spectrum and (b) realignment will be inevitable (possibly making your political affiliations no longer as valid as before, just like those of today don't match those of your parents or that of your grandparents). An important thing for each person to recognize is how they shouldn't keep ties to the political party of their past, solely out of habit or a feeling of loyalty, even as the general policies of that party shift away from your own.