Virtualization and Linux--A Primer (Part 2) - page 6
The commercial virtualization products are expensive, and as we Linux geeks are spoiled by the abundance of high-quality free-of-cost software, the idea of actually paying money for software can take some getting used to. The main differences between the expensive stuff and the free stuff are the management consoles and administration utilities, or perhaps I should say the lack thereof.
The commercial products all have excellent front-ends that can do everything: monitoring, cloning, provisioning, disaster recovery, scaling both upwards and downwards, and moving operating systems and applications around on both physical and logical servers. You get some fine-grained resource management, right down to CPU, memory, and storage allocations. There's a great little Virtualization Solutions Flash demo at Dell that shows how it all works.
For the free-of-cost set, Fedora's Virt-Manager for Xen is promising, but for now it has a very limited feature set. I've seen the odd PHP frontend here and there for different projects, but nothing I can recommend even for testing. (Hint to any bored FOSS coders looking for something to do: there's a good project to consider.)