For me, instancing has had very little appeal.
Within EQ1 they have made nearly, if not all, instanced zones accessible by groups only. That leaves the casual solo player unable to experience the zones. Within EQ2 they have addressed this issue and solo players are able to enter the zones and have an enjoyable time - similarly with DAoC. However, I feel that instanced zones have a very distinct feeling of isolation which robs the player of that important 'immersion' in the game world. Yes, it removes the issue of camping a specific mob as everyone can have his or her own mob to fight but the cost to 'believablity' is severe. With a game world that promises to have a rich environment I feel that there is no need for instanced zones.
Just my 2cp worth
