Also the other need for minimisation to prevent someone seeing what you're working on is not at all addressed. Possiblities: work involving confidential information, buying presents, demonstrating to someone that you're giving them your attention/stopping windows distracting people during conversaitons. While there's no longer a panel that things get minimised to, the 'minimise' button is effectively a hide-window operation that has several roles that aren't really provided in Gnome3. Unless you put it back of course.
You can also right-click on the title bar, and minimize is the first choice. It's "almost" as easy as a dedicated button, once you're aware of it.
- Mike