Apple's CFO Peter Oppenheimer alluded to it in the company's quarterly conference call Wednesday, although he didn't mention specifics - Apple isn't happy with its performance in Japan. On Thursday, it became apparent just who was the thorn in Apple's side: Sony.

In flash based devices, Sony has been able to best Apple for two straight months, knocking the iPod Shuffle into second place in both May and June. Behind this success is a new player from Sony that looks much like a perfume bottle and offers 50 hours of battery life with a 512MB or 1GB capacity in several colors.

Even more startling is the immediacy of the success. Sony went from a 4 percent flash market share in March to 27 percent in May and June. Meanwhile, Apple's share fell to below 20 percent.

While Apple still maintains a strong lead in hard drive based players with its iPod, Sony's success could mean that Apple may have the first viable rival to its business since it began dominating the industry last year.

Sony previously stunted its own growth by refusing to give its digital music players native MP3 support until last year. Analysts questioned the wisdom of the move, and even Sony executives later admitted that not supporting MP3 was a mistake.

But success in the US and Europe may be much harder to come by. Apple holds a 60 to 70 percent share of the market overall, a much stronger position than it held in Japan. Also, in the flash-based market specifically, the company holds over a 50 percent market share, again stronger than it was in Asia.

Also, more low priced audio players have flooded the U.S. and European markets. Sony's players are more expensive, with the player in question retailing for $150 USD for the 512MB version and $200 USD for 1GB of space. Apple's 1GB iPod Shuffle, meanwhile, costs some $81 less at $129 USD.