So, attached image profiles a few rocks made using various methods.
'A': These are sample Rocks from Andrew Price's collection. Looks very decent, easy to use and ready to use immediately. Downside is that the image plates used for texturing aren't available in larger (ie more detailed) sizes, so the resolution here is as high as they will go. (Confirmed that with a followup email to BlenderGuru).
'B': Some dude.
'C': rock made using internal displacements. I think this is how AP did his. (and yes I'm well aware that AP's experimental rocks are more realistic than what I've got here. It's the concept that counts
) It's extreme detail makes it first choice for up close, highly detailed ('Hero') images . And thanks to Kadri for explaining how to rotate a PF.
'D': A boulder that was made in Blender, imported into Terragen and externally displaced with a Power Fractal. Texturing done with an image file.
'E': Rock made using 123D-Catch (freebie from Autodesk). It's about 16 photographs of a single rock taken at various angles. The photos are uploaded to Autodesk website (it's free), are processed into a single 3D .OBJ file which gets downloaded to PC. Had to clean up the .OBJ file with Blender to get rid of image parts that aren't need, but result was pretty decent. It's detail and usability are about on par with sample rocks in 'A'. Only downside (besides lack of extreme detail) is that 123D-Catch is going away at some point and I haven't played with the replacement product yet.