I would like to just give my 2 cents of why I enjoy this service. In the past I never considered buying digital movies because for one the quality could never come close to blu-ray (heck, it barely reached DVD quality), and for another I didn't like being locked into a particular software/hardware eco-sphere (such as Apple or Microsoft products). But on the flipside I really wanted all my media in a digital format so I would no longer need the discs to watch them and also make them very portable, so I could do anything from watch them on any TV in the house or take them on the go, while still retaining top-notch quality.
My only option was to build both a media server with many TB of storage, along with an HTPC to stream it to my main home theater. After many years of wanting to do this, I just have never got around to it, mainly because I just haven't had the money to do it all. Not to mention I was dreading going through the whole tweaking process of making sure I was getting the proper quality.
With Vudu/UV these worries have been alleviated for the most part. I now have top notch quality with Vudu HDX, although not quite Blu-ray, especially with the audio, but close enough for casual viewing. If I want the best experience I still have my original Blurays. And now with UV, I don't have to worry about being stuck with one software/hardware company, plus I still have my discs to call my own. While I have to pay extra to transfer my discs over to digital, hopefully in the future all new discs will come with a UV copy free of charge, so this will alleviate any extra costs which will save in the long run compared to building a server/HTPC.