Yes. All intellectual property you work on, including in your spare time at home on your laptop, belongs to Google and you have to go through a reassignment procedure where they declare they're not interested in your work.

Which is okay if you work on one personal project at a time, but breaks down if you hop from project to project with friends. Waste of everyone's time.

Genuinely curious how enforceable it is, and how often it is enforced. That is, if you jump from project to project with your friends, on your own time and equipment, is there a legal case that despite whatever you signed its null? Similarly, how often does Google go after people like this?

I'd rather not end up in court against Google lawyers. Or generally have to work around agreements that I sign.