Query (duration) different between data value change

I am trying to write a query that would get me the duration of a status in a table. This query needs to work in SQL Server 2008.

Say I have the following table:

Key Value   RecordDate
1   1   2012-01-01
2   1   2012-01-02
3   1   2012-01-03
4   5   2012-01-05
5   5   2012-01-05 12:00:00
6   12  2012-01-06
7   1   2012-01-07
8   1   2012-01-08

I would like to get the following result

Value StartDate   EndDate     Duration
1     2012-01-01  2012-01-05  4 days
5     2012-01-05  2012-01-06  1 days
12    2012-01-06  2012-01-07  1 days
1     2012-01-07  NULL        NULL

Basically I would like the get the duration when of the value before it changes.

I am getting somewhere close, but still can't figure it out:

SELECT [Key], [Value],  
       MIN(RecordDate) OVER(PARTITION BY [Value]) as 'StarDate',
       MAX(RecordDate) OVER(PARTITION BY [Value]) as 'EndDate',
       DATEDIFF(day, (MIN(RecordDate) OVER(PARTITION BY [Value])), 
                     (MAX(RecordDate) OVER(PARTITION BY [Value])))
FROM [RateTable]
Order by RecordDate

I know that SQL Server 2012 has LAG and LEAD function, but since I am deal with SQL Server 2008, I can't use it.

Please advise

Here is the SQL statement that generate the sample data

CREATE TABLE RateTable(
    [Key] [int] IDENTITY(1,1) NOT NULL,
    [Value] [int] NULL,
    [RecordDate] [DateTime] NULL
    )
GO

INSERT INTO [RateTable] VALUES (1, '2012-01-01');
INSERT INTO [RateTable] VALUES (1, '2012-01-02');
INSERT INTO [RateTable] VALUES (1, '2012-01-03');
INSERT INTO [RateTable] VALUES (5, '2012-01-04');
INSERT INTO [RateTable] VALUES (5, '2012-01-05 12:00:00');
INSERT INTO [RateTable] VALUES (12, '2012-01-06');
INSERT INTO [RateTable] VALUES (1, '2012-01-07');
INSERT INTO [RateTable] VALUES (1, '2012-01-08');
GO

[Update] Thanks for everyone's inputs. I like to clarify a number of questions here, b/c I simplified many things here so that I won't add extra complexity to the problem that I am worki

This solution assumes there is only a single Value for each RecordDate. Performance will be better with tuned indexes, and probably breaking up the process using a temporary table or table variable. I used your script for test data. The output may not be exactly how you want it, but the process to get you close is what's important -- it works by filtering the rows to only the rows that start an interval, and then fabricates the end date by offsetting the results from the previous step.

WITH a AS
(
    SELECT
        Value,
        RecordDate,
        ROW_NUMBER() OVER(ORDER BY RecordDate) AS RN
        FROM [dbo].[RateTable] rt
),
b AS
(
    SELECT
        a1.Value,
        a1.RecordDate,
        ROW_NUMBER() OVER(ORDER BY a1.RecordDate) AS RN
        FROM a a1
        LEFT OUTER JOIN a a2 ON a2.RN = a1.RN - 1
        WHERE
            (a1.Value != a2.Value) OR
            (a2.RN IS NULL)
)
SELECT
    b1.Value,
    b1.RecordDate AS StartDate,
    b2.RecordDate AS EndDate,
    DATEDIFF(DAY, b1.RecordDate, b2.RecordDate) + 1 AS Duration /* Fixme? */
    FROM b b1
    LEFT OUTER JOIN b b2 ON b2.RN = b1.RN + 1
    ORDER BY b1.RecordDate;

Output:

Value StartDate EndDate Duration
1 2012-01-01 00:00:00.000 2012-01-04 00:00:00.000 4
5 2012-01-04 00:00:00.000 2012-01-06 00:00:00.000 3
12 2012-01-06 00:00:00.000 2012-01-07 00:00:00.000 2
1 2012-01-07 00:00:00.000 NULL NULL

StackExchange Database Administrators Q#46641, answer score: 7