Lots of people have written about the tools they used when writing and I would guess that writers have many different reasons for pursuing the perfect aids to composition. For me, it is partly a way of avoiding work but at the same time feeling like I am making progress. Just as a poor workman will blame his tools a mediocre workman looks for a crutch to help them limp along.
In 2008 I used Rough Draft for a while and it did help me think about the way some of the stories were structured and how all the bits should go together. A couple of things stopped me using it. Some craziness at work meant I fell off the wagon in terms of regular writing so did not have as much need for it. Now I have got back into it I have relied on Word because it is installed on every computer I use.
The other reason I stopped is because my working methods are so chaotic that it did not quite chime with that pattern of writing and revision. I think that is the reason that, so far, I'm a bit underwhelmed. That might be because I am only getting used to it and have yet to plumb all its features. There are some bits I like about it but so far I have only used it for a work in progress rather than a new project.
The downside is that it only works on the Mac so whenever I do have to do some work I'll have to use that. That is a problem because I don't think it will be easy to export a document prepared in Scrivener. Time will tell.