I'm getting a lot of horizontal screen tearing (Firefox 3.6 / Mac). This is especially noticeable in areas with floating chunks of earth. There is occasionally vertical tearing as well, though not as often.
Seem to be getting less tearing after upgrading to Flash 10,1,51,66 (Firefox 3.5.8/WinXP SP3). It still happens occastionally. Jumping around near the left side of NW Passage where the cave covered in grass is seems to do it 1 out of 25 or so times.
I had the same problem in Chrome. I have uninstalled and reinstalled the FlashPlayer beta release and will report if it still happens next testing cycle.
We also have some additional settings which work better in many cases (but worse in some cases) and will allow you to switch to those in the next testing cycle if you are seeing lots of tearing.