I actually played in the IBIS zm server yesterday n the day before that. I had often played in the IBIS WCS server and the rankings on there caused a lot of problematic issues among IBIS members as well as other players (Eg. I currently rank #1 in the WCS and the process of me getting there was ridden with f'ed up problems like jealousy and accusation)
So anyway, when i was in the zombie server the other day I noticed the ranks on it too. What i also saw were people complaining about sooo much more crap than other servers (I assume it is because when you die, your score is permanently recorded, therefore people are more "worried"[can't find right word] about their scores/deaths/kills) Rankings make the gameplay and gaming environment more serious.
So that is why I think you should remove the ranks. However, I think the addition of parachutes, zm vision, fast zombies, differnet zombie classes are awesome and they improve gameplay.
Just my 2 cents
