Christmas falls on December 25th every year.

That might seem obvious to you, but it appears the planners for some major corporations have been getting surprised by this. As you may remember, Barnes & Noble recently conceded that even orders for its “nook” e-reader placed before the Christmas delivery deadline November 20th might not make it in time for the big day.

Now Apple has acknowledged that its flagship 27 inch iMac may take two weeks to arrive, meaning anyone who was hoping to get one as a last-minute Christmas gift is out of luck. That delivery schedule compares with 24 hours for other models such as the next-largest 21.6 inch model.

The big question now is why the delays have arisen. Apple simply says “The new iMac has been a huge hit and we are working hard to fulfill orders as quickly as possible.” It certainly appears to be the case that the new model has been popular, with overall sales of Macs estimated to be up 74% across October and November (the 27 inch model having been released on October 20th.) While that would suggest inadequate planning and market research by the company, “excessive” demand is probably the least bad reason for shipping delays.

However, other sources suggest there may be a production problem with the model, with multiple reports of models having to be returned with a screen flickering problem (which is, of course, more of an issue with an all-in-one machine like a Mac.)

One website has put together statistics from nearly a thousand visitors who’ve bought Macs during the fall. Less than 25% were listed as being fault-free, though that can be discounted as people with a working machine have little incentive to go online to report the fact.

Of those with faults, the vast majority were the 27-inch model, and more than half suffered screen flicker. A week-by-week breakdown shows that models built in the last three weeks of November are considerably more likely to have experienced problems: one week had 156 problematic machines, compared with just one in the last week of September.

There are also reports that authorized resellers of Macs are experiencing significant delays in getting stock of the 27-inch model.