If you ever have written any Reporting Services reports off a cube (Analysis Services), and want to have a drop down that auto picks a day, this is for you. There is probably a more elegant way to do this, but it works.

=”[Time].[Calendar Date].&["& Year(DateAdd("D",-1,DateTime.Now())) &"-"& IIf(Len(Month(DateAdd("D",-1,DateTime.Now()))) < 2,Month(DateAdd("D",-1,DateTime.Now())),"0"&Month(DateAdd("D",-1,DateTime.Now()))) &"-"& IIf(Len(Day(DateAdd("D",-1,DateTime.Now()))) < 2,"0"&Day(DateAdd("D",-1,DateTime.Now())),Day(DateAdd("D",-1,DateTime.Now()))) &"T00:00:00]”

Remember, months and days need to have a zero in the front of them.