(as I only have 1000 chars....)

Will people game this, and will some dungeons be more popular than others? Of course. Fact is, the tanks/healers are already making a choice by leaving before the instance even starts, some are kicking the low level players who are the people they are being "rewarded" for helping, already dungeons are being favoured over others. However it should mean far more instances (no matter how long you waited for it) end up completed the first time.