I have a zillion DVDs and just got a blu ray player, am I going to replace all my DVDs with blu rays- no.
Will I stop buying DVDs? not completely but I will be more selective on what I do purchase on either format.. I can also download HD movies from iTunes and hook up my macbook pro to my HD TV so sometimes there won't be need to purchase a physical item. Although, it's interesting to note that some films are doing sets that contain dvd, blu ray and digital copy..