I am still having problems with caustics and photons. The bloody things never seem to do what I want. The whole collect on/off thing is confusing me to no end. I also learned, the hard way, that if a surface has the no_shadow property set, photons will not show up on it!
I also have tried writing photons to a file and then reading them back. However, when I read them in, they take as long to render as they originally did! Ahhhhhhg! There must be something else to set when reading them back in (like when reading radiosity data in... ).
I didn't even know you could write photons or radiosity data to a file. I gotta read the doc more often, instead of shooting in the dark, which I am guilty of sometimes. But, you know, sometimes I read that doc, and I just go, Huh? Like when some thing is an inverse square-root logrithmic function of that other thing.