I have not seen a single one of the issues you mentioned in any of the videos. I did not notice the audio skipping except the one video where someone opened an insanely large number of applications then tried to close some of them. Then you can expect a little skipping, as it swaps data around. But in reality, you are being a bit unrealistic if you plan to have 32 applications open at the same time and not the occasional skip.

Also how come you start by saying you have used an N900 briefly then go on to complain that in all the YouTube videos showing the N900 scrolling, it tears? Surely if you have used one you can comment first-hand if it did or not.

Anyway for me, ALL YouTube videos themselves a prone to tearing. In the one you linked specifically I can see tearing going on when they scroll the N900, but its happening to the WHOLE video, not just where the N900 screen is shown, so its clearly the video itself.