Think of it this way:
A dedicated server is up, 24 hours a day, 7 days a week (well it might go down occasionally for a few minutes if something happens on the server end, but you get the idea).
In that time, hundreds or perhaps thousands of players may enter and leave this server.
So there's nothing stopping the same people from logging into the DS every day to play and meet people, etc.
If there's a built in chat feature, then there you go, or else you can just talk in-game, it doesn't matter. You can talk to your friends on IRC or ICQ and agree to meet on the DS.
The other thing is that there will certainly be more than ONE ds. So just think of it as tons of games, that are on super fast public lines, that are up all the time.
So if you had a good connection (say at work or school or an extra computer) you could host a DS for your clan or something. You could play with your friends, or you could open it up to everyone, etc.
It would be much better than the Zone. With the Zone you could only launch games from it (although some of us IPers would just post our IP on the Zone for a game already in progress... but lots of people had been "dumbed down" by the Zone and didn't know how to join IP games, although all the info is in the game manual and countless websites).
The Zone's chat was also very primitive. It lacked most of the features that we've come to expect from IRC, even basic Java chat clients. People could flood with impunity. It was ugly, basic text. You couldn't mute people very well (they could just leave the room and come back, and spam you some more). Those popup messages were annoying too.
Anyway, it would just be a lot better, because 1) you'd have faster games to join 2) you could meet people on the same games and play as long as you want 3) there'd be less potential for MP cheating (well except for stupid client-side stuff like seeing through walls or full-bright, but that's stuff you really can't stop) and a remote admin could help regulate that stuff.
Anything is better than the Zone, with it's forcing you to 'upgrade' the software every week (and not fixing anything but minor bugs and adding more ads) and having hundreds of sysops with total power, but no code of ethics (hence totally arbitrary bannings, ignoring or hassling people of their choice, etc). Admin-Bots could do their job, 100x better as I see it, and that's what most chat rooms do nowadays.
Wean yourselves of the Zone, there are better things out there, and I'm sure people will be pleased with the new system JK2 will use.