Chat and the player list

One chat

A message typed on one server is seen on every server, looking just as it did where it was typed. Team chat and blocked chat never cross servers.

One player list

The tab list shows everyone on the network, with their rank title before their name (sometimes as a picture; see Your rank). /players (or /online) lists them too. Neither ever shows which server anyone is on, so nobody can track a player down that way.

Joining and leaving

"Steve joined the game" appears once, when Steve joins the network, and "left the game" when Steve leaves it. Moving between servers is never announced.

Coming back

Log off on one server and you log back in on the same one. If that server is down, you arrive at spawn instead of being turned away.