Multiple group support

For me it's THE future who make punbb hard to admin.

An user can only be member of one group and it's a problem !
i.e :

They are 3 users : Paul, John and Mike. They are 3 forums : Sex, Drugs and Rock'n'roll.

Sex is public, evryone can read it. The two others are private rooms.
Paul can read Drugs but he's not allowed to read Rock'n'roll.
John can read Rock'n'roll but not Drugs.
Mike can read all but he's not an admin or a moderator, he's a "normal" member.

I make groups "drugs readers" and "rock'n'roll readers".
Paul is a member "drugs readers". He can read "drugs". It's good.
John is a member "Rock'n'roll readers". He can read "Rock'n'roll". It's good.

But Mike can not be a member of two groups ("Rock'n'roll readers" and "drugs reader") so he cannot read "Drugs" and "Rock'n'roll".

Maybe there is a solution but I don't know.

Please change the code to allow users to be in many groups (need a new table "Groups").

If Rickard is OK I can code this the next month for 1.3.
Tell me what ...