True skip-levels just for the sake of meeting/networking with the group, I'd say I've done a few times a year everywhere I've worked. At my current job I talk to my boss's boss at least once a week, though and my boss's boss's boss has a monthly group meeting with his whole org. At my last job I routinely presented in meeting 4 levels above me (just under CEO), but that was for specific work, not just to meet and mingle.
At my last company, pretty much any time we had a skip level, his boss would show up too, so we'd have a skip-skip-level.