Have been pondering this and have come up with an alternative that uses a Tally table:

DECLARE @d1 datetime, @d2 datetime

SELECT

@d1 = '20090101',

@d2 = '20090331'

SELECT

count(N)

FROM

Tally

WHERE

N <= DATEDIFF(day,@d1,@d2)+1

AND

(DATEPART(dw,DATEADD(dd,n-1,@d1))+@@DATEFIRST)%7 BETWEEN 2 AND 6

Advantages over previous solutions, as I see it, are:

- Doesn't use CTE's (recursive or otherwise) or ROW_NUMBER, so can be used in SQL 2000.

- The query itself is a lot simpler to read

- Looking at the query plan 92% of the time is spent doing a clustered index seek.

- Use of @@DATEFIRST and Modulus operator makes the solution multi-culture

- Use of BETWEEN rather than NOT IN is significantly quicker