Declare @Start DATETIME2,
		@End DATETIME2 = DATEADD(ms,-3,CONVERT(DATETIME2, CONVERT(DATE, DATEADD(DD,-DATEPART(DD, GETDATE()-1),GETDATE()))))
SELECT @Start = CONVERT(DATETIME2, CONVERT(DATE, DATEADD(DD, -DATEPART(DD, @End)+1,@End)))
SELECT @Start, @End

Select CONVERT(VARCHAR(4),DATEPART(MM, start))+'/'+CONVERT(VARCHAR(4), DATEPART(DD, start)) AS [Date], 
		COUNT (DISTINCT Username) AS uniquelogon 
from Miview
Where Activity = 'Logon'
and Start BETWEEN @Start AND @End
GROUP BY CONVERT(VARCHAR(4),DATEPART(MM, start))+'/'+CONVERT(VARCHAR(4), DATEPART(DD, start))

SELECT STUFF(REPLACE('/'+CONVERT(VARCHAR(5), YourDate, 101), '/0', '/'), 1, 1, '')

GROUP BY CONVERT(VARCHAR(10), YourDate, 101)

ORDER BY DATEADD(d, DATEDIFF(d, 0, YourDate), 0)

DECLARE @Miview TABLE
    (Username VARCHAR(20), Start DATETIME, Activity VARCHAR(20))

INSERT INTO @Miview
SELECT 'Tom', '2012-09-07 12:00', 'Logon'
UNION ALL SELECT 'Fred', '2012-09-07 12:01', 'Logon'
UNION ALL SELECT 'Fred', '2012-09-07 12:02', 'Logon'
UNION ALL SELECT 'Tom', '2012-09-05 12:00', 'Logon'
UNION ALL SELECT 'Fred', '2012-09-05 12:01', 'Logon'
UNION ALL SELECT 'Sam', '2012-09-05 12:02', 'Logon'
UNION ALL SELECT 'Bob', '2012-09-05 12:03', 'Logon'

DECLARE @Start  DATE = '2012-09-04'
    ,@End       DATE = '2012-09-08'
    ,@Days      INT

;WITH Tally (n) AS (
    SELECT TOP(1+DATEDIFF(day, @Start, @End))
        ROW_NUMBER() OVER (ORDER BY (SELECT NULL))-1
        FROM sys.all_columns)
SELECT [Date]=STUFF(
        REPLACE('/'+CONVERT(VARCHAR(5), Start, 101), '/0', '/')
        , 1, 1, '')
    ,UniqueLogins=COUNT(DISTINCT Username)
FROM (
    SELECT UserName, Start=DATEADD(d, DATEDIFF(d, 0, Start), 0), Activity 
    FROM @Miview
    WHERE Activity = 'Logon' AND Start >= @Start AND Start < DATEADD(day, 1, @End)
    UNION ALL
    SELECT NULL, DATEADD(day, n, @Start), 'Logon'
    FROM Tally) a
GROUP BY Start
ORDER BY Start