Kreacher knows the locations of all the horcruxes, I'm sure.
i 'll only get into it if you guys really want me too, but I figured out (as I'm sure others have) that kreacher assisted Regulus Black (who HAS to be RAB) in fuckin' with those horcruxes.
I'll say this: if you've read book six, when Harry and Dumbledore go across the zombie lake, Albus tells Harry it's a clever trap because two people HAVE to go, not one, but that the boat will detect two WIZARDS.
He basically says that both he and Harry could get in the boat because technically Harry isn't a wizard yet, and isn't powerful enough to be detected by the boat.
Since I'm sure Regulus was the one setting the traps, we can reasonably assume that Kreacher was his assistant. Why?
Because there was a motherfucking horcrux in the Black house in book 5. YUP. Hanging from a mirror.
Look it up. I did. I control+f'd my was to this deduction using pdf files of the books. lol