This is what Macy Gray said about John in an interview following-up the release of her new album, Covers (just what it says it is).
Q: You’ve collaborated with George Clinton, John Frusciante and Mos Def. What do you like about working with other artists?
A: I’m like, “How did you get so good?” You can’t teach what John Frusciante does. And you definitely can’t teach how to be George Clinton.
And here's the entire interview, for everyone who's interested. :)