Doubts in a Glenn Berry Query ( CPU per Database )
On first glance this looks to me to approximate CPU per database, over the history of sys.dm_exec_query_stats (so usually since the last restart), but only for plans that are currently in the cache. It also relies on a plan cache attribute, dbid, which means that was the context for the query, but not necessarily that that was the database that caused the work. For example, guess where all the CPU gets reported for this query:

USE tempdb;
GO
SELECT CONVERT(DATETIME, CONVERT(CHAR(10), CONVERT(DATE, 
  CONVERT(DATETIME, o.create_date)), 120))
FROM msdb.sys.all_objects AS o
CROSS APPLY model.sys.all_columns AS c;


I'll give you a hint: It's not msdb or model.

So, it should be used as a ballpark, but there are no guarantees that it reflects 100% of reality 100% of the time. The more often you query it (e.g. have some automated job that stores snapshots of it every n minutes), the more accurate it will be, but unless you have applications that treat each database like impenetrable silos, it will still be influenced by database context rather than the actual source of queries and data.