I just read on ThinkSecret that Quartz 2D Extreme is disabled by default in Tiger. http://www.thinksecret.com/news/0505q310q.html This is major. It means Tiger has a whole lot of graphics performance that is hidden. You can enable it by installing the developer tools and running the program /Developer/Applications/Performance Tools/Quartz Debug. It is in the Tools menu. I have an NVidia 6800, and it makes a big difference when e.g. resizing a Quicktime window.