It’s a bit tricky at first (watch the tutorials, they’ll save your ass), but once you play around with it for a bit to get the hang of it, it’s pretty sweet.
I love love love that it has a corkboard feature; I can organize my story bits on it, and rearrange them at will. I like to do a decent outline (which means you don’t have a lot of reordering to do), but having the ability to move stuff around without losing anything is great. I can also have multiple panes open, so I can have a list of character names on one side and my current WIP in another (incredibly handy).
When you’re done, you select all the bits you want to include, hit ‘compile’, and it puts it all together into one file, saved as .txt or .rtf or whatever of your choice. And if you don’t like the way you put it together? No problem, the orginal file hasn’t been deleted, so you can go and redo it as many times as you like.
On the downside, which isn’t really a downside, the wordcounter is off from that used by the nano site, so writing an additional 500 words is wise.
My biggest negative is that I can only use it at home; I use a computer at work but it’s not ‘mine’, so I can’t download Scrivener onto it, and I don’t have a tablet or laptop.