This post is just as a reminder to the msdn links and for those that are not aware.
There are a number of built in methods that can be used on SSRS reports. Such things as formatting numbers, getting current user etc.
http://msdn.microsoft.com/en-us/library/ee874032.aspx
http://msdn.microsoft.com/en-us/library/cc570403
These can be used in the expression in the design of the report.
Here are some examples:
=Microsoft.Dynamics.Framework.Reports.DataMethodUtility.GetFullCompanyNameForUser(Parameters!AX_CompanyName.Value, Parameters!AX_UserContext.Value)
=Microsoft.Dynamics.Framework.Reports.BuiltInMethods.ToDisplayStringAmount(Parameters!AX_RenderingCulture.Value, Sum(Fields!Balance02.Value), true)