Congressional approval rose sharply in the months after President Obama's inauguration, from 19% in January to 31% in February and 39% in March. Approval then began to slip gradually, dipping to 31% by the end of the summer, before falling precipitously in October. Given the current 21% reading, it appears that any "honeymoon" period for the 111th Congress has eroded.
To be honest, I'm surprised that it's that high. I would rate Congress' grade as an F.
Of note is the steep decline in approval among Democrats, who appear to be souring on the job Congress is doing despite the fact that their party controls both the House and the Senate. For the first time since February, Democrats' approval of the job Congress is doing is below 50% -- with only slightly more than a third of Democrats now approving.