I give the DVD copy to friends who have not upgraded to HD yet. The blu-ray disc is the preferred media used for playback if possible. I have a blu-ray player in my living room and a blu-ray drive in my laptop, so I rarely run into a situation where I can't use the BD. I do use the included digital copies as this allows me to watch the movie on my iPad if I'm on the deck or traveling and don't feel like lugging my laptop around, or, if the battery on my laptop is low and I don't have access to a power outlet. When possible, I redeem the digital copy from iTunes as this allows me to download the movie and store it locally. I keep the original copy on my laptop and back it up to my portable wireless hard drive. This way I don't have to worry about limited storage space on my iPad or having to pick and choose which movies to sync to it, or what kind of internet connection I have available. Instead, I just make a direct wireless connection between the portable hard drive (with it's built-in wireless routing capabilities) and my iPad and stream the movie locally. In the extremely rare situation where I can't use the BD and I wasn't able to redeem the digital copy from iTunes (mostly only an issue with Warner Brothers films), I have the fallback of streaming from Vudu or Flixster as I maintain my UV library with both services.
I can't foresee a situation where I couldn't use my BD copy and couldn't access my iTunes or UV copies. I still own a bunch of movies on DVD that get used on a fairly regular basis, but only because I don't have an HD copy of those movies, yet. For anything that I own on Blu-Ray, I have absolutely no use for the DVD copy of the same movie.