I have tried Fotoxx (under Ubuntu 10.04) and some functionalities are very user friendly, see here :
http://kornelix.squarespace.com/fotoxx/
http://kornelix.squarespace.com/fotoxx-gallery/

But the best way is to try Fotoxx to better see some interesting behaviors.
... so i think it would be interesting if XnViewMP could also have some functionalities like:
\Retouch:
Brightness and color adjustments using movable curves
Flatten brightness distribution (quick fix for many photos)
...
\Area:
Select Area Mouse
...
\Tools:
converts one or more RAW files to tiff-16 format

...
...???