Horowitz was a great exponent of the Clementi Sonatas and there is an amusing story (Harvey Sachs, Rubinstein , A Life page 353) peripherally regarding them. A few days before a certain concert was to be performed on February 3, 1975, Daniel Barenboim, (pianist and at that time, conductor of the New York Philharmonic) received a message from Horowitz that he needed to see him. Barenboim had no idea as to what Horowitz wanted. Barenboim arrived at the appointed time and was received by a very "formal " Horowitz. (Horowitz opened the door), They sat down and talked about many things including Horowitz' Berlin days.. Barenboim recalled, He told a lot of stories—very one sided, Im sure, but it was still a lot of fun. Then Horowitz said, Tell me, you know Clementi Sonatas? Not really. Barenboim replied.. Horowitz then played several of the sonatas pointing out various fascinating figurations. None the less, Barenboim still wondered why Horowitz had requested the meeting. Barenboim realized that several hours had passed, and since he had to attend a rehearsal the next day, he informed Horowitz that as much as he had enjoyed the evening, perhaps he should take his leave. Horowitz replied, No, no, no. Stay. We're having a nice time and Wanda is not here: shes playing cards. (Then) in a sort of forced, intimate tone of voice, he said, Tell me, I read in newspapers that you are conducting with Rubinstein, with Phyilharnonyic. What he plays? I said, he's playing Beethoven G Major and Brahms D Minor.
Oh, in one evening? He's an old man now, no? He doesnt forget?
I said no
But wrong notes he plays, no?
I said Look, I played with him in London, the Emperor Concerto, a few months ago, and it was note perfect. (I lied!).
He said, How much strength? You know, an old man, he has strength? These are big pieces!
I said Yes, you can't cover him with an orchestra.
He said, This is very strange: an old man; no memory lapse, no wrong notes, lots of strength. (Long pause) But a little bit dry, no?

Barenboim concluded the story saying, "It had all been for this. Not much later, I had lunch with Rubinstein and told him the story in great detail. He was very amused." ..