About two-thirds of iFans eligible for a free upgrade to what Apple calls “the world’s most advanced mobile operating system” have apparently chosen to skip it entirely -- at least for now.

That’s a rare stat for the world’s most valuable technology company, whose extraordinarily passionate users are traditionally eager to adopt anything and everything Apple.

More than 100 million users have upgraded to the new iOS 6, the software powering the company’s iGizmos, Apple said last week. But according to analysts at data research firm Strategy Analytics, 173 million iPhone users, 85 million iPad users, and 25 million iPod touch users are eligible for the upgrade -- -- 283 million in all.

Which means 183 million have said “no thanks.”

Consumers may be skipping the upgrade for a range of reasons, explained Ross Rubin, principal analyst with Reticle Research.

'They could be in contract for a phone that can't update to iOS 6 or have a model that can't take advantage of some key features...'

— Ross Rubin, principal analyst with Reticle Research, explaining why some may not upgrade immediately

“They could be in contract for a phone that can't update to iOS 6 or have a model that can't take advantage of some key features and therefore choose to hold off,” he told FoxNews.com. “Or they could have heard of the problems with the Maps application and choose to hold off until it improves.”

Apple’s home-grown replacement to Google’s Maps has been criticized for failing to live up to Apple’s billing as “the world’s best mapping app.” Apple CEO Tim Cook issued a public apology on Friday for the software, promising quick improvements.

But in a 28-page thread on Apple’s message board titled “downgrade iOS 6 to iOS 5,” many users lament the loss of YouTube and Google Maps nevertheless, and debated a return to the older system.

“I was uber excited for iOS6 because I thought the new map and Siri on my iPad would be worth it -- but I can't do anything on my iPad without having the battery life drained quickly,” one user wrote. “I'm not happy nor amused Apple. Please fix it.”

Others were more direct in their criticism.

“I want to be able to downgrade my iPad to iOS 5. Apple, this is ridiculous!”

An article on enthusiast site Mac Life even offers tips on how to make the switch back to iOS 5. The site offers links to older software packages from Apple’s servers, which users can use to “restore” their system to an earlier state.

Not everyone is upset with the new software, of course. Several users said they were willing to live with the little bugs, assuming a fix is in the works.

“I upgraded to IOS 6.0 and found all these bugs and decided to downgrade to 5.1.1. But now I missed those new features, and guess what, I upgraded back to iOS 6,” one user wrote on the message board.

“I don't mind the bugs, I know they will be fixed soon, and I have workarounds to overcome them.”

And Apple customers actually upgrade more frequently than users of Google’s competing platform, said Neil Shah, a senior analyst with Strategy Analytics.

“Though it looks slow, the iOS 6 upgrade [rate] is definitely faster than the competing platforms such as Android,” he told FoxNews.com.