We have a SQL Server 2008 R2 (10.5) on a dedicated box with a single 2.4Ghz processor, which regularly runs at 70-80% CPU. We are going to be adding a significant number of users to the application and therefore want to add a second processor to the box (scale up).

Will SQL Server automatically use the second processor to balance threads, or is there additional configuration that will need to be done? In other words, will adding the second processor drop my CPU usage to 35-40% per CPU, automatically balancing the load?

Based on what I read here, it seems that it will: http://msdn.microsoft.com/en-us/library/ms181007.aspx

However, I've read elsewhere that CPU performance gains can be made by assigning database tables to different filegroups, but I'm not sure we want to get that complicated at this point.