Very good points at the start of the article and I may do some refresher readin on some bits but for the specific example would something like this not be better?

CREATE PROCEDURE [spSearchPeople]

@firstname nvarchar(50) = '',

@lastname nvarchar(50) = ''

AS

BEGIN

SELECT ID, FirstName, LastName FROM People

WHERE FirstName LIKE '%' + @firstname + '%'

OR LastName LIKE '%' + @lastname + '%'

END