I just read a nice, modest quote from Chopin about his only two teachers: "Under Zwyny and Elsner the greatest donkey could have learned." (btw, found this in Chopin: A graded practical guide - good book).

Any other quotes or anecdotes about the relation of famous pianists/composers with their teachers?

Hummel said when he was studying with Mozart as a kid, Mozart would frequently interrupt whatever musical studies were going on and make him play a game of billiards. Hummel also got punished once for ripping a hole in the cloth on the billiards table with his stick (which doesn't seem very nice; I don't think the poor kid did it on purpose).

The image of little Hummel ruining Mozart's billiards table makes me laugh...

Liszt about Czerny: "That good master to whom I owe both my talent and my success."

Richter about Neuhaus: "He was my second, musical father.".

And here is a nice one about Chopin, from his student Mikuli:

Teaching was something he could not easily avoid, in his capacity as an artist and with his social attachments in Paris; but far from regarding it as a heavy burden, Chopin dedicated all his strength to it for several hours a day with genuine pleasure. Admittedly he placed great demands on the talent and industry of the student. There were often "lecons orageuses", as they were called in school parlance, and many a lovely eye left the high altar of the Cite` d`Orleans, rue St. Lazare, in tears, yet without bearing the least resentment against the greatly beloved master. For it was this rigor so hard to satisfy, the feverish intensity with which the master strove to raise his disciples to his own pinnacle, the refusal to cease in the repetition of a passage until it was understood, that constituted a guarantee that he had the pupil's progress at heart. A holy artistic zeal glowed through him; every word from his lips was stimulating and inspiring. Often individual lessons lasted literally for several hours, until the exhaustion of master and pupil own out.

Wilhelm Backhaus studied with d'Albert (insofar as d'Albert could be said to have been a teacher; he was more of a coach), but d'Albert did not like Backhaus because their temperaments were so different: Backhaus being a perfectionist; d'Albert, like Anton Rubinstein, an artist for whom the great conception was what counted. A story goes that Backhaus's cufflinks brushed the keys when he was playing for d'Albert, and that d'Albert thereafter said, "His cufflinks were the only thing that clicked with Backhaus."

:D

I can imagine the constellation of those two to be very 'special'. I have read a compelling description about the 50-year old d'Albert which may contrast with the perfectionism of Backhaus:

(trying to translate from German)
"Within the hall - 2000 people in delirium. The playing - fuzzy, imprecise - 100000 missing notes, shaky rhythms... but the experience as a whole is like an earthquake, a tornado, the crashing of two planets, the sun in a devastating blast of fire. I was standing on my chair (actually I was standing on my head), cheering in enthusiasm with all the others: 'What a genius at the keyboard'."

A famous pianist/teacher (but I can't remember who!) took a group of his students to hear D'Albert play. The tyros spent much of the performance grimacing and sniggering at all the mistakes they were hearing but were chastised afterwards by their teacher who told them that he would rather hear a handful of wrong notes played by D'Albert than a thousand of his pupils' "correct" ones.

Who wrote the description in the previous post?

Busoni (I think). He told them 'if only you could do mistakes the way he does.'....

Who said this one?

pianoloverus, in case you mean the quote I gave, it's from James Huneker . It's quoted in a German book on piano literature (similar to the Hinson's).

That will never happen again in these times

I believe the Busoni quote was, "if only you could make such mistakes." Priceless.
There's also a wonderful description by Grieg upon hearing his ballade played by D'Albert--he really must've been something to behold.