I bought my iPhone on MacWorld day, since there was no announcements of an update then. Unfortunately that was just over the 14-day return policy window. Not that I'm completely sure I would have replaced it anyway. Thankfully the extra space is also an extra $100 (if it was the same price, then I would have REALLY been pissed). And 8gb is enough for me...for now. Of course the SDK might change all that. But either way, I don't mind switching out media all the time -- I do it a lot now anyway.
More room isn't a big enough deal for me. I don't think I'll switch to a new iPhone until there's a version with a much better camera, and perhaps a 2nd camera on the front for videoconferencing. (I assume 3G will also be part of an upgrade -- which is nice, though not as essential for me...)