The 27-inch iMac's shipping lead-time has been reduced again; it's now down to 5-7 days from the time you place an order. The shorter turnaround time indicates that manufacturing of 27-inch iMacs is getting back up to speed after a slowdown that Apple says was caused by unusually high demand.
Courtesy of Apple
While I think it's true that 27-inch iMacs are one of the most popular iMacs in recent history, there have also been a few problems with the model that forced Apple to make engineering changes, in the form of firmware updates to correct two known issues. The first issue was screen flickering. I saw this firsthand, on a 27-inch iMac we received in early January. The flickering occurred randomly, as a horizontal line stretching across the display. We ended up having Apple replace the iMac. So far the replacement has had no issues at all.
The second problem reported with some 27-inch iMacs was a yellow tint to the display. While we never saw this problem, it produced a lot of comments on Apple's Discussion site. Both issues seem to have been corrected with two firmware updates.