I use nvALT (http://brettterpstra.com/projects/nvalt/). It's a Notational Velocity fork that syncs with SimpleNote. Since it saves the notes in text files, I have put them in a Dropbox folder. The notes directory is itself a git repo which is committed every hour with a cron job on my laptop. It's actually working out pretty well. I have double backup (Dropbox and Simplenote) with infinite versions through Git. If any one of these services loses my notes, I still have them on my laptop. I could also push it go Github, but I haven't gone that far yet.
However, this setup doesn't do pictures and audio notes, but I don't really need them very much.
I don't think it's a good idea to store a .git folder in Dropbox. Dropbox doesn't know how to resolve conflicts deep in git internal files and will break your repository.
I love nvAlt though. Been using it for years and never had any data loss.
I actually had my entire workspace in Dropbox for the fear of losing data, and Dropbox handled git fine. As long as the files are small enough, Dropbox does a great job of getting the file up as fast as possible so that conflicts generally don't happen.
Since most of my changes to the notes happen on one device (my laptop), I have never had any conflicts. Using nvALT on different computers sharing the same notes folder through Dropbox does have some problems which the nvALT website recognizes as well.
However, this setup doesn't do pictures and audio notes, but I don't really need them very much.