All humor aside, Nick's response hits the nail on the head: you use blades when high rack density is a requirement. Generally speaking, there is no real efficiency gain--everything you mention is already possible with various management software, KVM switches, good network design, etc. You're just paying a price premium to have all of that in one (relatively) small box.
You also have a new single point of failure: the chassis. Now, instead of one server going down because of a hardware fault, you can lose ten all at once. Personally, I think you'd have to be nuts to build a cluster out of blades, unless your cluster was sufficient size that it spanned multiple chassis and losing multiple boxes at one time was an acceptable failure mode.
Conclusion: If you're looking for an application for your blade servers, instead of looking for blade servers for your application, you have purchased the wrong hardware.