The one major thing to remember about the clouds as opposed to terrain is there is *no displacement*. Cloud shape is based on Density Shader input, which by default is connected to a fractal noise type function. Trying to apply displacement to the clouds directly won't work; neither will trying to apply *displacement* to the noise shader connected to the Density Shader input.
To affect the cloud shape you'd need to work directly on the color values of the Density Shader's input node. This means your Warp, or any other shader you want to affect cloud shape, should be connected to the default Density Shader power fractal node, or at least connected to this Density Shader input (which interprets color values as volume).
Remember that displacement will have no effect, your changes will only be those that happen in color space, so mess with what's on the other tabs and ignore displacement - all the other settings should have some effect. You can either use the main Input connection of the default Density Shader to get a mix, or use the Blend Shader to get a kind of "masking" effect. The Warp effect is setup a bit differently but again it needs to interact with the color values of the default Density Shader, so keep that in mind.
Granted the options for working with clouds aren't as powerful as they could be, but you still have a whole lot of flexibility if you know how the system works. Simply assuming it works like terrain (e.g. using displacement) is the biggest misunderstanding most people have. Hopefully the above will get you to a point where you can at least experiment successfully.
- Oshyan