Michael could go on and on about server consolidation (as he often does), but I made him keep his editorial, "VMs vs. Multiple SQL Server Instances" in the December 2007 issue short to make room on the page for my picture. :) Luckily, we didn't have to squeeze all the information onto that tiny page. You can learn more about server consolidation options and get help deciding which is the best solution for you from the following resources:
Virtualization:
"SQL Server Virtualization FAQs"
"SELECT TOP(X): Virtualizing SQL Server"
"What You Need to Know About the Virtualization Format War"
"Virtualization in the SMB Market"
"Check It Out: Virtualization Is Free For All"
"Market Watch: Virtualization Products"
"VMware Workstation and Server Differences" (live on Web 11/28/07)
Multiple SQL Server Instances:
"An Instance of Understanding"
"Inside SQL Server: Managing Multiple Instances"
"Inside SQL Server: Multiple Instances"