This update resolves issues that may affect some Windows Vista-based computers. These issues have been reported by customers who are using the Error Reporting service or Microsoft Customer Support Services.
By applying this update, you can achieve better performance and responsiveness in various scenarios. This update also improves the reliability of Windows Vista.
This is the update leaked about a week ago now officially released by Microsoft. I don't have any doubt that it's fixing things but like I reported, I have not noticed any performance differences in my Q1.
[Via Origami Project Forum]