Of course, the results depend on what's in your collection, and how good your tagging is.
Songs bought via i Tunes come replete with tags (click on a track and choose Get Info from the File menu to edit or add tags) and many from commercially-released CDs also get tags added as you import them.
Basically, it states that when you opt-in to the Genius feature, Apple will automatically collect information to be used to identify media in your i Tunes library on your computer including your play history and the contents of play lists ...
This information will be stored anonymously and not associated with your name or i Tunes account.
All of those CDs, tracks from other sources and tracks from i Tunes and other sellers have created am impressive music resource.
It's not guaranteed though - I got no results for Beethoven's Symphony 7 by the Auckland Philharmonic, downloaded as a podcast from National Radio, and Arnold Schwarzenegger calls Gateway got no suggestions either (OK, it's a prank audio file using samples of Terminator dialogue).
It could also give Apple phenomenal leverage over record companies.
Apple says it won't - the whole issue is spelt out in your legal agreement you 'agree' to when you install i Tunes.
With Genius, click on any song you like, then press the Genius button to get a list of suggested matches.
Hopefully you'll be pleasantly surprised and rediscover some gems.Apple insists the information will not be used for anything apart from generating Genius playlists, but think of the potential for this information.