Well, that depends on your point of reference, really.
I play the Irish whistle (which in itself isn't always a well-tuned instruments, especially the cheapies) and it's been hard getting the rest of the mini orchestra I play in for church to accept it. Nice as it sounds, I can't seem to match the pitch with the other instruments on a note-by-note basis. Some people tell me that every note is a little "out of tune" and has to be handled differently from other notes in order to play in tune, if at all possible. "Some people", I say, because there are others who tell me that the instrument is not tuned to the Equal Temperament tuning system which pianos and most other orchestral instruments use. There are whistles that come in Equal Tempered tuning, of course, but others use Just Intonation. The latter differs from the former on a note-by-note basis and could be the reason why my whistles seem out of tune with other instruments.
But Equal Temperament is a compromise system, so, in a sense, you can say they are out of tune. In an effort to create a tuning system where music can be easily transposed to different keys without sounding out of tune, Equal Temperament was developed. It is most prominent in pianos, which need to be able to play in all different keys without the need for retuning (which could be helluva lot of work!) between playing different pieces. It is a compromise because in order for it to work, some notes are tuned in a way that they don't sound "perfect" (they may be sharp or flat based on other tuning systems).
So too bad for me. I can't control my whistles that perfectly as to vary my pitch to match the other instruments for each and every note (and my hearing isn't trained to that level yet to be able to tell pitch differences very well), if at all possible. And I can't afford the more expensive whistles that come in the imperfect Equal Tempered tuning. Maybe the problem is everyone else is "out of tune" with me. Haha... But I guess in this case, the majority wins.
(Some information on tuning systems here).
