I use this report on PokerDIY to check how many new users I have had each month and the average per day over each month.
SELECT DATENAME(m , CreatedDate) as Month, YEAR(CreatedDate) as 'Year', COUNT(*) as 'New Users', COUNT(*)/(SELECT day(dateadd(mm,datediff(mm,-1,CAST(MONTH(CreatedDate) AS NVARCHAR) + '/' + '01' + '/' + CAST(YEAR(CreatedDate) AS NVARCHAR)),-1))) as 'Ave Users /day'FROM Users U
INNER JOIN UserPortals UP ON UP.UserID = U.UserID
WHERE PortalID = 6
AND Authorised = 1
GROUP BY DATENAME(m , CreatedDate), MONTH(CreatedDate), YEAR(CreatedDate)