I dont see how anyone can seriously think that the P4 renderer is anywhere near firefly in terms of rendering. Firefly may not be the best in its class, but it has a node based shader system, supports multiple threads (and rendering in a separate process), AO and IBL, support for HDRIs, as well as 64 bits if you have PPro. All of these are big improvements over P4.

P4 is better then firefly in what ? Less wear and tear on your CPU ??

Also this:

Quote - But...., on the other side it's impossible to render real clouds with raytracing!!!!....

Is totally wrong. Most apps that do volumetrics, use what is called raymarching (or volumetric ray casting), a modified version of raytracing. It's modified in that it not only calculates the start and end points of each 'ray' but also over the path the ray travels. This let's you take 3D procedurals and render them as solids of varying density, giving you a basic 'cloud.' That's how everything from vue to mentalray to lightwave does it.