Comment by spydez

They did not.

Well, they did originally have "who's online" functionality, but they had to yank it when someone found an exploit, and it took them forever to get it working again.

The "email me" option was much later - around the time they went from "Preview" to "Beta", I think. And as thorax said in his reply to me, Google flubbed the UI/usability of the preferences.

As far as "who has a Wave account", it's the same scheme as email. You get a Wave address; you're responsible for letting all your friends know what your address is (e.g., mine's in my HN profile). Probably could've been improved by hooking into Facebook/Twitter/etc. and spamming out your Wave address to all your friends...