Hello Mark,
Just a few points:
1. I, personally, don't like all the movement on-screen. You obviously do! But there you go... we are all different...
2. The left hand edge of the screen is tight up against the left side. I would prefer to see a margin there, much the same as you have elsewhere.
3. Ooops... just noticed that the right hand margin is flush against the right hand side too, when you have a very wide stretch of text.
4. Apparently the prefered width of text is about 65 to 70 characters. This width makes it easier for visitors to read the text on the screen, much the same way as the columns in a newspaper make reading that easier. It is documented somewhere, but I can't remember where.
5. I only have a small screen, and therefore have to scroll horizontally... not my favourite pastime! But when I do, I notice that some of the retangles don't align along the right hand edge.