There have been strong rumors about new iMacs appearing at the October 23 event, and we’ve seen no better confirmation of that so far than shipping times from Apple slipping across Europe. The UK is now at 1-3 days, while France is even worse at 3-5 working days (click for full size).
However the short supply is seemingly affecting only certain European countries (Spain still has them in stock), and the US isn’t affected either.
Nevertheless, I would take this as a clear indication that Apple is preparing for a refresh. Whatever you do don’t buy an iMac before October 23rd!