The recently announced iMac has proven to be pretty popular with customers. So much so, in fact, that the 27 inch version of the iMac, initially shipping in December, is now in so much demand that any new orders will not ship until next year. The change is now reflected in the US Apple online store where the shipping estimates note that new 27 inch iMac orders are not available until January.
This is not reflected in some international stores, however, as for example, the UK online Apple store is still listing the 27 inch iMac as shipping within 3-4 weeks, meaning that any new orders could still be delivered in December (potentially!). In addition, the 21.5 inch iMac has greater availability both in domestic and international stores, with most order shipping within 7 to 10 days.