This function is about 100 times faster:

IF EXISTS (SELECT * FROM sysobjects WHERE name = N'DecimalPlaces')

 DROP FUNCTION DecimalPlaces

GO

CREATE FUNCTION dbo.DecimalPlaces

 (@A float)

RETURNS tinyint

AS

BEGIN

declare @r tinyint

IF @a IS NULL

RETURN NULL

set @r = 0

while @a - str(@A, 18 + @r, @r)  <> 0

begin

 SET @r = @r + 1

end

RETURN @r

END

GO