Some things you learn about and then proceed to forget about them. This is one of those cases for me. In fact I posted about this Vista performance tip what seems like ages ago here on GBM. I thought it was worth fresh look so here we go.
The round Start Button or Orb can cause the GPU to force a non-rectangular clipping operation when it is overlapping a maximized window. This indeed causes some performance issues, especially on lower end graphics hardware. The best way to remedy the situation is to resize your Taskbar so that it is double height, which encompasses the Orb.
I long ago had forgotten about this and the taskbars on the Tablet PCs I use and test were all set to the default single row height. While at the MVP Summit, we were all comparing things we do and don’t do to improve performance and this tip resurfaced. It was one of those D’OH, slap yourself in the forehead moments then. Since returning home I’ve been doing some testing on this and I’ve noticed that on both the Lenovo Thinkpad X61 and the HP tx2051, it makes a significant improvement in screen redraws when I swivel the screen from laptop to Tablet mode.
Here’s the link to the original tip on the Tablet PC Team Blog. You’ll need to scroll all the way to the bottom of the article to find it.