I only see my own connections/processes in the new activity monitor... whereas in the earlier versions of SSMS you could see everyone's. Do I need to change a setting or something?
YOu will need VIEW SERVER STATE permission to view the Activity Monitor in SQL Server 2005 and SQL Server 2008.
Under the processes make sure you have select Login as (All) to show all the processes. BTW do you see any of the system processes?