at this point, i prefer to do all of my practice away from the piano. (just kidding. now i'm wondering about the person who said this to me - so long ago. i thought they were serious).
say, bernhard, you said later 7 +or- 2. so, being the math whiz that i am - i thought, 'ok, five or nine.'
now, what i do is combine all the good advice i get into one big snowball. my grad teacher tries to cram 5 -6 -7 things into one 'repetition.' i'm thinking about hand position, sound, relaxation, fluidity, etc. etc. - but usually i can only think of three things whilst doing one repetition. so i repeat it again to do the other three things.
now, if his way of being efficient is to do the minimal work to get to the point of 'learned' - i would try to do five repetitions and see if the sixth and seventh could be nixed. thereby, shaving off untold hours of practice on say a piano concerto.
in reality, for me i only practice what seems difficult and only repeat those passages. if everything else is fairly easy - i just play it once or twice and go on to another piece of music.
i have learned that i can listen to myself better when i play along with my own tape recordings. it sets things in my head that might usually take more 'repetitions' to memorize. maybe it is teaching me to TRUST my ear.
agreed with everyone. lostinidlewonder said it well about too many repetitions. then, you have a hard time making it sound 'spontaneous.'
**also, perhaps the exact number varies on the difficulty of the passage and the student. i'd probably expect grade 1-8 students to repeat things three times. slow, medium, and fast as they could handle without mistakes. for excellent students - it would be a refinement of that (patience allowing) to be slow (largo/processional), moderately-slow (slow walk), moderate (jog), fast (run), super fast (presto/sprint), superfulously fast, prestissimo. or, if a slow passage - refining dynamics and sound each time repeated. counting more and more accurately. you can see how far you can divide each beat (beyond 1 and 2 and...) or even (1 'e' and 'a' 2 'e' and 'a') to (su -gar -coa-ted- can-dy can give you a d d)