I actually tried to negotiate a sabbatical after five years before coming to the new gig (particularly since I’d just given one up leaving Amnesty at the end of three years). No dice. Great little talk on the benefits of taking time out from work.
Of course, what happens is I just take mini-sabbaticals in between jobs though would really like to plan for one in a few years time from this gig (though often think I am kidding myself that I’ll ever take time off properly - when will those books get written?).