fastone RAW viewer ?

Why do my RAW files look great in fastone and then lose all of their life and go flat when I open with LR or CS4?

FastStone is almost certainly showing the embedded preview jpeg, which will show the effect of the in-camera Picture Style and other settings.

Without some processing there would be no image to see, but LR/ACR default processing is much more conservative than the camera's. Funny thing is that although most newbies are put off by that, I have also seen posts where people complained that the LR defaults are Brightness 50, Contrast 25 and Black 5. They argued that everything should be at 0, darker and flatter.

I have installed FastStone Image Viewer 4.0 and I agree that it is displaying just embedded JPEGs in RAW files. In every RAW file there is embedded JPEG even if you are not shooting with the setting RAW+JPEG. I've made this conclusion from 2 observations:

1. full screen preview of RAW file is loaded instantly, but it usually takes a few seconds to decode RAW data.
2. producers of digital cameras usually oversaturate colors when creating JPEG from RAW data. But RAW Processor let a user to set the level of saturation while an initial level is always lower then camera's one.