I tried sake last year. I got fed up with crushing cooked rice, so I tried an earlier method of preparation called bodai-moto. The result is a carboy full of lacto-sour sake. I felt a little better when I read Sandor Katz talk about sour sake in Art Of Fermentation. It's still waaaay tart to drink (at least for me. I'm not a sourhead...yet), so I'm going to try using it to start a Berlinner Weisse or maybe put some in a boil to do a Guinness-style partial souring on a big beer.
Rice preparation was a big mess. I'm still not 100% sure I had all the koji propagated properly. I'm thinking about doing a batch with black or red koji, just so that I can see it properly when it grows.
My LHBS is out of sake kits, so I'm going to try gemcultures.com for my koji. It's cheap, so I plan to overpitch a little.
One thing I was wondering about is what effect the ratio of koji rice vs non-koji rice has on the finished product. Does having the non-koji rice control the fermentation speed?