You have a large scene requiring a lot of stones and rocks and you would like to avoid the tedious work of making them one by one ? This setup is made for you :
http://3d-synthesis.com/tutorials/StonesFactory.blend
Stones Factory is a setup allowing procedural creation of stones and rocks with texture, in few clicks. The provided blend files already includes on several layers textures that can be enabled or disabled to create a large choice of stones textures. You can add you own textures and shaders to create any kind of rocks.
Dont know if your are going to read this ever but let me tell you that you have done one of the most clever and useful things I have ever seen in Blender. Awesome!!!