Assuming you're not a jerk, expect your friends list to gradually grow. When opened, you can view each friend's current status and warp directly to them if they're online. This should make it easy for groups of friends to locate each other to start questing. It does seem like it's best to quest with people you know, since not everyone has Wii Speak or a desire to chat regularly, and you can never be sure if someone's just joining up to screw around. If someone does have Wii Speak hooked up, you'll be able to see it with an onscreen icon, and you can enable or disable mic chat as well as voice volume.
- IGN
I'm guessing Wii Speak is just open chat where available, friend or not.