Ask Slashdot: What type of asset would you not virtualize?

An anonymous reader writes: With IT and Data Center consolidation seemingly happening everywhere our small shop is about to receive a corporate mandate to follow suit and preferably accomplish this via virtualization. I've had success with virtualizing low load web servers and other assets but the larger project does intimidate me a little. So I'm wondering: Are there server types, applications and/or assets that I should be hesitant virtualizing today? Are there drawbacks that get glossed over in the rush to consolidate all assets?