As for Rondo, he's hurt at the moment and its really effecting his defense.
Prior to his injury his defense has mostly been good this year, with some serious lax stretches and other excellent games. (he did a great job denying OJ Mayo for example any jump shots and the ball for entire quarters)
I do think that he's a much better defender when his minutes don't creep near 40, you can see him get tired and when he's tired his bad defensive habits occur more often.