This afternoon I've been reading a rather enjoyable mystery (from a NY house). I found myself suddenly yanked out of the story, however, when the heroine began listening to Beethoven's Moonlight Sonata on a classical music station. Why? The sonata was being played by the London Philharmonic. Immediately my reading came to a screeching halt.
"How could it be played by the London Philharmonic?" I thought, puzzled. "Wasn't the Moonlight Sonata written for unaccompanied piano? Or am I wrong?"
It was a very minor point in the story, but my curiosity was piqued. Dropping the book, I went downstairs to my CD collection. Sure enough, the CD I have indicated it was unaccompanied. I trotted back up the stairs and Googled, finding a useful entry at Wikipedia, which states "a piano sonata is a sonata written for unaccompanied piano," and lists the Moonlight Sonata as a notable example. Certainly our heroine might have been listening to a transcription for orchestra, but unless that's stated outright, it appears to any reader familiar with the music that the author simply didn't know her facts. It pulled me right out of the story and caused me to start searching for information.
This is not what you want your reader to do-- the reader should remain buried in your book from start to finish. Anything that yanks the reader out of the story is undesirable. So when writing, even if you think you know something, make sure you check your facts!