We've just completed a seamless, relatively quick upgrade to our older, original iPhone. This update went without issue at about 7PM EDT. While this is not a blanket endorsement to go ahead and upgrade your phone, it appears that Apple may be on the down side of the issue.
We'll take some time with the 2.0 software and write a brief review. Assuming that upgrading is really a no-brainer here, we won't spend all that much time on it. We noticed a number of odd error messages during the day with our older software. For example Visual Voicemail returned an "unavailable error" on one of our units consistently throughout the day.
Hopefully, all of these issues have been resolved. Good luck with your upgrade to iPhone 2.0.