As part of the European Space Agency Summer of Code in Space 2011 two new features were added to the Stellarium planet rendering:

Procedural perlin noise (fBm) clouds.
Bump mapping with normal maps on ellipsoid planets.

The code was implemented in C++ and OpenGL using GLSL shaders and the Qt Framework and it requires a shader model 3.0 capable graphics hardware. The development branch is on launchpad.

Relevant posts:

"New Stellarium Features"
"Improvements in Stellarium Planet Rendering"

Screenshots and Videos:

The cloud color, velocity, darkness, sharpness and scaling are parameters and can be modified through Stellarium configuration file (ssystem.ini) to look more real!!

earth new features — Screenshot of Earth (bumps, clouds).

moon new features — Screenshot of Moon (bumps).

Stellarium running on Mac OS X.

A brief introduction to normal mapping can be found in Wikipedia.
The Perlin Noise solid textured clouds are described in [1] and [2]. See also this website

Related Papers:
[1] Ken Perlin, "An image synthesizer", SIGGRAPH 1985
[2] Ken Perlin, "Hypertexture", SIGGRAPH 1989

Serres' FOSSCOMM 2012 Presentation:
[3] Serres' 2012 FOSSCOMM presentation (in greek)

Code:

https://code.launchpad.net/~hikiko/stellarium/socisplanet

Many thanks to my mentor Fabien Chéreau, Alex Wolf and the Stellarium development team for giving me the opportunity to participate in the ESA SOCIS, as well to the organizers of the summer of code! Also, special thanks to James Hastings-Trew for his textures and bump maps.