Thanks for the comment Ramiro. A few answers:
#1 Yes, I definitely teach my students to use GitHub, Subversion or similar for projects, but not in CS1. I usually save introduction of these tools until second year courses.
#2 Unless you do some magic, the user has to remember to commit to trigger the revision control features of GitHub and similar. For most cases, the backups are not automated which leads to the backups just never happening. (Aside: how many people reading this have multiple backups of the computing device they are using now to read this comment?)
#3 The majority of my students (and colleagues) use Dropbox everyday but do not know about this and other features (like recovering deleted files/directories).
Another technology that many already have but do not know it is the auto-backup using Time Machine on their Mac OS computers.