I'll start my first real post on this blog with the following: a few weeks ago Microsoft released Service Pack 1 for SharePoint Server 2010. So why is it important for PowerPivot? It drastically improves performance for PowerPivot users!
In SharePoint 2010 Service Pack 1, members of Excel Services were able to cut the number of ECS query requests nearly in half, which means half the load on PowerPivot application servers per user action and therefore almost double the PowerPivot scalability.
You can find more details about the Service Pack here, you can also download it directly here.