I regularly or semi-regularly log into ten Linux boxes, one of them my own. SSH keys help, but really solve the wrong problem.
I've worked in an NIS+ environment before. It was kinda nice, but fragile. And it was very annoying we couldn't mix FreeBSD and Linux; the NIS+ protocol is closely dependant on how the systems locally do things like password storage. No surprise, Linux and BSD diverge there.
Wade.