Yahoo! Inc. (NASDAQ: YHOO) and SanDisk Corp. (NASDAQ:SNDK) are launching a new MP3 player with WiFi capacity, joining a host of rivals to Apple Inc.'s (NASDAQ: AAPL) iPod, including the Microsoft Corp.'s (NASDAQ: MSFT) Zune.

The iPod currently has 70% of the portable music player market, and, that number appears to be holding. If the iPhone sells well, Apple will have another horse in the music download space. Cellphones that can download music are offered by the large handset manufacturers including Nokia Corp. (NYSE: NOK) and Motorola Inc. (NYSE: MOT), but there is little evidence that they have done any damage to the iPod's growth rate.

As much as it must pain Apple's competitors, no one has been able to throw anything in front of the company to slow the momentum of the iPod and its download service iTunes. The European Union recently announced that it would look into pricing issues involving iTunes and the record companies. That may eventually hurt Apple just as antitrust actions by the EU have slowed Microsoft's progress on the Continent.

Apple's only enemy appears to be its own success.

Douglas A. McIntyre is a partner at 24/7 Wall St.