My game runs fine in general, but I have experienced it lagging a bit after I've played a level for a short while.
The main problem though is that when I first start up the game I always have to go into a level and quit out of it – if I don't, there is a terrible buzzing noise while I'm playing a level and the cutscenes run at an incredibly slow pace (I still haven't been able to watch the opening cutscene at all!).
I also had the same problems with the Brownie level as Cecek. I got past it by restarting the level and it worked that time. Not sure why. The salt was also flashing for me as well.
There are absolutely no options to adjust the quality or controls, which I think is really bad. And yet some of you are talking about "setting it to -ultralow". Is that a command line thing? Because if so I really can't be bothered with that shit. Integrate it into the goddamn application, for heaven's sake.
Anyway, I'm running OS 10.6.8 on a Macbook Pro with 2.16 GHz Intel Core Duo and 2 GB of RAM, and using the DRM-free version from the Humble Bundle, if that helps.