Virtualization is being adopted in many different environments and situations. If you are a developer, virtualization can provide you with a contained environment where you can safely do almost any sort of development safe from messing up your main working environment. If you are a systems administrator, you can use virtualization to more easily separate your services and move them around based on demand.
The default virtualization technology supported in Ubuntu is KVM, a technology that takes advantage of virtualization extensions built into Intel and AMD hardware. For hardware without virtualization extensions Xen and Qemu are popular solutions.