I don't see an advantage with the iPod shuffle (heck, it has no screen) But the iPod nano and the full iPod might benefit. Certainly, if the long-rumored "true" video iPod ever sees the light of day, it could certainly take advantage of Mac OS X just as the iPhone does. Plus, Apple benefits from reducing code bases to manage.

In fact, here's how Apple's web site describes the iPhone and Mac OS X: "All the power and sophistication of the world’s most advanced operating system — OS X — is now available on a small, handheld device that gives you access to true desktop-class applications and software, including rich HTML email, full-featured web browsing, and applications such as widgets, Safari, calendar, text messaging, Notes, and Address Book. iPhone is fully multi-tasking, so you can read a web page while downloading your email in the background. This software completely redefines what you can do with a mobile phone."

Of course, it's uncertain exactly what version of Mac OS X the iPhone uses. There are no menu bars, windows, mouse cursor, etc., as in the "traditional" Mac OS X. And the iPhone OS X has goodies Mac users haven't seen in Mac OS X: multi-touch screen support, on-screen "smart" keyboard, cellular phone networking, drivers for the iPhone sensors (proximity, light, accelerometer). In other words, as John Gruber has pointed out in a Daring Fireball [url=http://daringfireball.net/2007/01/os_x]column[/url], the iPhone’s version of OS X contains everything from Mac OS X that’s applicable to a mobile phone, plus new bits specific to the phone. It’s a "full" version of OS X not because it contains everything from Mac OS X, but because it contains everything you’d actually want from Mac OS X, he notes.

Chicago Sun-Times columnist Andy Ihnatko got to spend some time with the iPhone in January and [url=http://www.suntimes.com/technology/ihnatko/215441,CST-FIN-Andy18.article]wrote[/url] that "everything I've learned (both in official briefings and 'you and I never spoke, all right?' sort of discussions) says that it truly does run Leopard, the upcoming 10.5 OS that will be released for the Macintosh late in the spring."

And Daniel Eran in a [url=http://www.roughlydrafted.com/RD/RDM.Tech.Q1.07/081A0C60-AD28-40EE-89EE-D54F1024FDBB.html]Roughly Drafted article[/url] has postulated that iPods may have used a subset of Mac OS X code for some time already, in secret. Apple has never made any comment on what operating system existing iPods run, ever since the company moved from Pixo, the operating system that ran the very first iPods, he notes. If that's true, Apple may be ready to reveal that Mac OS X software, ported to the ARM processor architecture, has actually powered iPods for years.
 
"Making that information public now would only be necessary if Apple decided that it was the time to open development for the iPod family, starting with the iPhone," Eran says. "Up to this point, iPod development has been shrouded in secrecy, with only a select few developers allowed the details needed to produce 5G iPod games. The internal structure of iPod games suggests that at least the 5G iPods use an Apple designed, custom system. It would make sense that Apple would attempt to reuse as much code as possible from existing development on Mac OS X. Will Apple release, as a familial companion to Mac OS X, an iPod OS X?"

Regardless of what OS the iPods have been using so far, the thought of future models sporting the OS X that runs on the iPhone is intriguing. What new features might it offer? How would this affect battery life?

Doubtless these questions will be answered well before year's end.