Checking SQL Server's memory utilization Is there a way to check how much of the memory reserved by SQL Server is actually being used by SQL Server?

Is there a way to look at this information in the past? I.e. how much memory was being used an hour ago?
You can run DBCC MEMORYSTATUS at any time (or probably better to look at the sys.dm_os_memory* DMVs). 

As for getting the data from an hour ago, that would require some kind of collection using a monitoring tool, MDW, etc. SQL Server doesn't keep snapshots of memory utilization for all of time - that would get pretty expensive.