I'm using SQL Server 2008 RTM and connecting to SSMS as sa.   The SQL Server 2008 Activity Monitor is missing some columns such as host, net library, net address which are in SQL Server 2005 Activitiy Monitor and most columns such as database name, task state have no value for many rows.  Am I missing something completely?  I'm running the same application in both SQL Server 2005 and SQL Server 2008.

Activit Monitor is similar to the Task Manager view that you will see on windows operating system, you can add the columns as per your requirement and if possible try to view the same using another client's machine.