Don't know about iMacs, but I just checked the ship times and all dual PowerMacs are 3-5 days here in the US. On the 17th I had saved the PowerMac page from the Apple store and all said same day shipping.
Now every mac yes every mac on the US apple store has 1-3 days or 5 days as it's shipping time...
On a side note I read that all the new PMs that are allegedly shipping on AI (http://www.appleinsider.com/article.php?id=1024), and on the UK apple store only the single 1.8 PM has a 25 shipping time, all the others are 5 days!
Extreeeeeemmmllly wishful thinking but I can always hope!