Hi Andi,
I think you miss the point about cloud computing: Cloud computing is a style of computing in which dynamically scalable and often virtualised resources are provided as a service over the Internet (or another network). (see wikipedia)

It has nothing to do with a "central server" and actually doesn't resemblance the "classic mainframe client-server model" at all. Just read the description on amazon ec2:
... is a web service that provides resizable compute capacity in the cloud.

If you use a client/server architecture on it, or peer to peer, or independent monolithic instances which work on a common result doesn't really matter.

Cloud computing enables me as a developer dynamically scale and assign computing power and other resources to my application. This is also what RightScale provides.

So please explain me, how should that be a reincarnation of the classic client/server model? It neither defines client nor server, it isn't centralized (its a cloud, like the internet and not like a central mainframe).

As I see it, it need not necessarily be a mainframe
that's hosting the cloud services. It could be a
cluster of cheaper computers. The main thing is
that whatever's hosting the cloud application, needs
to be fast