Virtualization is just the beginning
Virtualization is just the beginning of the complexity. Hybrid-cloud deployment, shared services with software-cost-allocation, and growing use of mobile devices and usage-based licensing schemes are making it ever harder to both stay in compliance and to cost-effectively purchase only what's needed. Keep in mind that what's licensed, what's installed and what's actually used are three, distinc things, and they're often wildly out of sync. If you've installed or are using more than you've licenced, you're out of compliance and may face steep fines if uncovered by an audit. If you've licensed software that's not being used (whether it's installed or not), you're paying too much and you could strike a better deal.