I agree, the 250gb HD seems to be the cause of the holdup. I ordered a 17"/SD/AE/BT/250gb on 8/31 and I still have a shipping date of on or before 9/29. A friend of mine ordered a stock 1.6ghz model about a week and a half later and it was delivered yesterday.
Comments on the combo drive model: it's beautiful, the quality of the 17" screen is dramatically better than the one on my parents' iMac G4. It was a bit loud though, a sort of annoying mechanical whine when the fans got going under heavy processor load. I don't understand the woes about the "chin," it didn't strike me as particularly obtrusive. My friend was switching over from an ancient HP desktop that was on its last legs (with Windows 98). His reactions were what seem to be par for the course: "Where's the computer?," "it's so quiet" (even though I was thinking it was too loud) and "the screen is so bright." He got an iPod mini and is just delighted with it, and while taking a tour of the bundled software he discovered GarageBand and is probably out buying a keyboard to use with it as we speak.
It seems that for a fairly large population of people, raised with Windows and yet not terribly conversant with computing, the combination of virus problems and an itch to join the iPod crowd are making the iMac a very attractive switcher's machine.