OK, let's see, 8+ hours later and I'm downloading.
The links that came in with the iPhone DC sign-up are dead. Generally they either state that a server can't be found, or they send a "sorry" message.
I looked at some of the failures Safari was reporting, and as usual, some of them simply didn't make sense, including one complaining that the server connect.apple.com could not be found (I could ping it). For some strange reason after confirming I could ping the site, I just typed in that url, and it brought me to the usual ADC sign-on screen, or so I thought. This time after entering my info it asked me to read/sign a user agreement from January (one I remember agreeing to before). This time when I agreed, I was dropped into the iPhone site and was clearly signed on.
So I'm happy now, downloading the SDK with a few minutes to go.
Really sounds like one server talking to another server and getting lost in the translation.
Hope others have better luck than I have.