multiple vs single instances

I have a question i would greatly appreciate any input on. I am a dba handling 4 instances, some with multiple databases. All running on one server with databases ranging in size from one gig to six. My question is what would be better, to continue on our current path- creating a new instance for each contract tuning each as needed or to run just one instance containing all of the database tuning just one instance for maximum performance. aside from the obvious problems such as larger single backups, and if one goes down they all do what are other potential problems or better yet perks? please offer any insight you may have. Thanks in advance. -----------== Posted via Deja News, The Discussion Network ==---------- http://www.dejanews.com/ Search, Read, Discuss, or Start Your Own