Hi Chris,
The CR Viewer works 'offline' when it is not connected to the CR Server/BI Enterprise.
Meaning, reports need to be saved 'with data'. You should be able to:
1) Drill down into groups, subreports
2) Change prompt values - works when the Record Selection formula is moved to the 'Saved data selection formula'
3) Export to various formats
To 'refresh' data, it needs to be connected to a BI Enterprise.
-Abhilash