DECLARE @YourTable TABLE
(Cust_ID INT,Date DATETIME)

INSERT INTO @YourTable 
SELECT 1,'2008-12-05' UNION ALL
SELECT 1,'2008-12-08' UNION ALL
SELECT 1,'2008-12-25' UNION ALL
SELECT 1,'2008-12-28' 

DECLARE @MyTable TABLE
(id INT IDENTITY(1,1),Cust_ID INT,Date DATETIME)

INSERT INTO @MyTable  (Cust_ID,Date)
SELECT * FROM @YourTable


SELECT DISTINCT a.*
FROM @MyTable a
	INNER JOIN @MyTable b ON b.id <= a.id
WHERE DATEDIFF(dd,b.Date,a.Date) > 4