Dimo is working on this neat VRay plugin. It allows you to create the most fab rocks, coral, sponges etc. from a userdefined proxy mesh.
Although I haven't found the right way to lower rendertime, there's definetely some strong potential in this one. And I'll be tweaking a bit to find out more.
It's open beta so far - make sure you get the right version for the right version of VRay.
Here is a very nice CGsphere that Dimo did last year using his own plugin.
Old test :
