I compose all my books in Google Docs. After I'd been writing for three years or so, I read an article by some writing pundit who claimed Google Docs was second on his list of good platforms to use. Armed with this confirmation bias, I have never looked elsewhere. It's easy to use and [bonus] backing up my work is something I rarely remember to do [what could go wrong? It's Google. :-) ] My publisher, however, demands that all work is submitted in MS Word. Google Docs easily transfers over, but then when my editor and I trade versions back and forth I have to relearn all those skills. I really don't like it, but hey, this is a small price to pay.