You can now download movies the same day that they become available for sale on DVD through Movielink or Cinemanow. Looks the prices are normally around $19.95 while (even though I hate them) Wal-Mart offers titles as low as $14.99 the first week that they are released.
I would be concerned about backing up the downloads in case of a hard disk crash as well as whether or not there is an DRM/oddball extra copy protection on the downloads. Personally I will stick to the cheaper route of buying the DVD at the store. With freeware programs on the market that can break DVD copy protection, one could upload from the DVD to a laptop or other PC and still have the original in a secure location.