Recently, we were looking into when someone had updated some management packs and when.  I went digging a bit and found the following query helped me out.  Run it against the OperationsManager database.

Here is the plaintext code:

SELECT TOP (1000) [MPName]
      ,[MPVersion]
      ,[MPCreated]
      ,[MPLastModified]
FROM [OperationsManager].[dbo].[ManagementPack]
ORDER BY [MPLastModified] DESC