At PDC last fall, "we discussed how real world browser performance involves many different subsystems (see video below). Different websites use these subsystems in different ways, and to build a fast real world browser you've to start by understanding these overall patterns. This post provides an inside look at how these subsystems impact the performance of five real world websites. Internet Explorer 8 for this analysis, and as IE9 approaches we'll talk more about how these performance characteristics evolve," said Micrsoft.
More Info: IE team blog