I've got Scrivener. It's very good as you can use as much or as little of the fancy features as you wish. The best bit is that you can just set up a plain writing screen that is very easy on the eye and distraction-free.
My problem is that I migrated in a novel that I had already written 250 pages of... so I had to muck about with setting it into chapters and whatever. If you use it from day one and plan it all out properly it would be great.
Another problem (for me) is that they've just updated it... the new version is supposed to be easier and more intuitive, but I'd have to update my MAC OS before I could download it. I'll get round to it one day.
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Steve J
Unkind tongue, right ill hast thou me rendered
For such desert to do me wreak and shame