I think it depends. If you're working on something with a hard upcoming deadline, chances are you have no 20% time. If you're working on a launched product in incremental/maintenance mode, chances are you have extra time.

Sometimes greenfield projects or rewrites also permit lots of 20% time, because you've got existing implementations, so you can have some people maintain the old one and some people go work on the new rewrite using new tech.

I'm one of the unlucky ones with very little free time at the moment. :)