Two days ago I returned from Christmas vacation, and during a period of two weeks I have not had the access to a piano. Instead I have spent the time chopping wood and clearing away enormous quantities of snow.
Returning to the piano was a bit frustrating. I had a feeling that my fingers were replaced by wooden sticks, and that I was playing really badly. However this feeling gradually disappears, and already now I think I'm back on my normal performing level. Moreover I find that some of my memorising stuff has matured, and that I can play at least one new piece from memory now.
So maybe absence from the piano of a week or two doesn't need to be a big problem when comes to maintaining the repertoire. Does anyone else have similar experience?

Yes, I took a week off in June, Ganddalf, and spent the time thining about how I go about practising and digesting all I've learned here in the forum and on piano sites in general. There was a marked acceleration in progress following the break.

I have always taken the occasional week away from the piano and always found it a convenient time to reassess my skills, aims and progress. The time away is usually so beneficial that now I leave the weekends free always for work on memorised repertoire and unfinished pieces that I haven't touched for a while and stop the learning process for a couple of days to let it sink in more.

I also tend to work on four 'groups' of new pieces and work one week on and three weeks off. I haven't reached a definite conclusion about its value but it does seem so far to be better than sticking with a piece for too long at one time and most definitely faster than sticking with a piece until it's finished.

Horowitz, I think, was tongue in cheek.

I have similar experience. Practicing every day sometimes does not seem to help me to advance. After a break of several days some things suddenly seem to work - even fine. I for a moment have to find finger feeling again, but then am surprised that I advanced by having had the break.

I think this is because the brain needs time to little by little become reprogrammed with what we by practicing asked it to succeed with. Once brain circuits have had enough time to interconnect better optimized on piano playing, playing piano results optimized. I assume that this is the reason that learning to play piano needs long time, and not only much practicing. We need to frequently trigger the brain optimization process by practicing, but also need patience to let brain optimization processes happen.