DVDs are not going anywhere. I would say they have twenty years or more left in them at least.
I'm digging the blu-ray and HDs, but I won't be replacing my entire collection.
I'll buy movies I don't already have OR stuff like Star Wars, Superman, Raiders, Trek, James Bond that need great picture and fantastic sound. Action and sci-fi flicks will benefit most from these new formats. A friend of mine has Unforgiven and said it looks astounding.
As for regular DVDs, many older films have just arrived and may not make the upgrade. I'm still waiting for Rolling Thunder and Monster Squad to hit DVD.
With the machines being back-wards compatable there's no excuse in not having one of these beauties, with the exception of the insane pricetags.