In a general sense, a change happening on a vast scale. A shift in the big picture, if you will.
Specifically "The Paradigm Shift" refers to a certain oft discussed and theorized shift in social groups concerning several different intersecting social circles. The Paradigm Shift did not happen within the originally proposed timeline of the spring of 2008, but new evidence has come to light suggesting that The Paradigm Shift may still be happening, just on a larger timeline and consisting of not exactly the same changes as earlier expected.
"The Paradigm Shift" may still come to manifest itself in the first quarter of 2009.