Just been going through a Deep Dive Workshop with Lars and some of the other members of the Microsoft team and discovered the following...
When creating a simple 2 dataitem report - eg. Customer & Cust. Ledger Entry we were trying to include a boolean variable on the Request Page to suppress the printing of customer records when the customer has a Balance (LCY) = 0.
To do this we need to add the variable (including the label) to the classic report sections before opening the report in the Visual Studio designer. We can then use this flag in our visibility expression.
Make sure that the boolean is added to the section to which it relates - in this case the Customer dataitem (as this is the group for which we are setting the visibility expression in this case)! If the boolean is added to the Cust. Ledger Entry section on the classic report, and yet we are trying to make use of it in our Customer group in the visual studio layout, there will be no effect and all customers (regardless of balance) will always be shown.
I suppose it does make some sort of sense, but it is something to watch out for :)