I write short stories and novels in my spare time and I have to honestly say the best writing software I've used is a simple text editor. In Windows 7 I use a full-screen text editor called JDarkRoom and once I finish I copy-paste the text onto MS Word/LO Writer and then begin organizing the novel with that.
For notes I usually write them down on a piece of paper or make a text file and then I use XMind to plan the novel.
I've tried Scrivener demo for Windows and yWriter and I have to admit I'm far more distracted trying to organize everything and I never get to actually writing.
But hey, whatever works for the individual.