Last week third party retail sources began to report that iMac supplies were dwindling making it difficult to replenish stock. This was despite the online Apple store and retail stores showing ample supply. Whilst Apple's online store still shows good stock of the iMac, rumours now suggest a refresh as soon as next week.
Today 9 to 5 Mac reveals that Apple has begun notifying customers that their orders are being pushed back a week:
Due to an unexpected delay, we are unable to ship the following item(s) by the date that you were originally quoted:
Z0JP, IMAC 27/5750/SD
will now ship on or before
May 02, 2011
A separate report from Mac Rumors states that Apple is planning a change in promotional material for Tuesday, May 3rd.