I installed Mavericks OS (10.9) on Mac a day or two after it was released. (It was free and I'd skipped Mtn. Lion.) Since then, I think I am seeing AM's GUI acting less responsively. That is, I see the time-cursor stuttering slightly in Southpole and Arpeggiator, for instance, even if I have only three or four contraption windows open at the same time. I cannnot prove it, but I don't believe this used to be the case. I can't remember seeing this kind of not-so-smooth movement before, except perhaps when I had a large number of windows open at once.
(Knowing Apple, they've diddled something somewhere just because they can. They managed to rearchitect how Safari handles sound, I know, thus making a great program called Audio Hijack Pro cease to be functional with that browser. On purpose?)