Matt asks about playing from memory:

>More generally, is this a practice that is common among performers that
>I've simply never noticed?

Well, from my 20 od years of concert going, I can only remember 1 or 2
occasions wen a piano solist has had a score in front of him/her on the
grand.  I would think that it is/was a thing that developed during 20'th
centrury, piano solosit being vain, did not want to be regarded as lesser
musicians than string soloists (whom been scoreless for much longer).

It's become a trend with conductors as well, to lern things at heart - to
be able to skip the intimidating score.  I heard the young Russian/American
conductor Yakov Kreizberg two weeks ago doing Shostakovich eleventh from
memory - quite a stunning performance, kept me two inches above the seat.
- British pianist Imogen Cooper played a woolly Mozart 27'th from memory as
appetiser at the same concert, which put me to sleep...  But it was from
memory...

peter lundin, gothenburg.se -  Counting the days: DSCH 100 (1906-2006)