I dont experience that, but I do notice that I get a lot of random lag spikes. They don't occur enough for me to get mad at them, but they have made me lose new records I get on my songs. Sometimes when I use DT on some maps like Crayon Pop - Saturday Night (Hard), the approach circles appear laggy, but switching applications with command-tab and then switching back a few times will magically make it stop happening. (Or maybe it's just that restarting the map fixes it after doing so a few times).
I only really get the bad lag Tsuchi is talking about when something pops up with Mac's stupid application update message. Sometimes Mac's message 'loads' but doesn't appear for a few seconds, so I'm left wondering what is making my game lag. I open activity monitor, and see the update task and then I just end it, and the mac update message appears for a split second before just disappearing, and then my game is not as laggy anymore.