Mission-critical applications need to be reviewed strategically before they are virtualized in order to ensure their success. In this post, Mark Vaughn also notes the importance of using monitoring tools to measure response times, performance metrics and other key performance indicators:
If an application slows down the week after it is virtualized, no one will acknowledge that the performance is normal during month-end processing. All that users will know is that you virtualized the application and now it is slow. Have before-and-after snapshots to defend against these attacks or to troubleshoot the valid issues that may emerge. The more granular the reporting, the better.
Check out the full post, What to Consider Before Virtualizing Mission-Critical Applications, from SearchServerVirtualization.