kris, Most of the free for alls I have been in have been mostly instrumental sessions but, either way, I think you will find that most people are able to just work things out amongst themselves and don't want to dominate. As for evening itself out, I think it does in terms of people getting a fair share of what they want to do on a given night - someone maybe bursting to sing a few or on exceptional form one week, not feel like doing much the next...

When you do get the very shy person, it does help if those with more experience try to encorage and maybe invite them to do a song or tune. As for the hoggers, it depends on the group but in my experience, one of the stronger members of a group is likely to jump in quickly and play or sing strongly, maybe there are some looks given, a song may get a cold reception, etc. the "offender" gets the message and with luck balance is restored.

Jon