Well aside from the borked iPhone 3G launch, it seems that the MobileMe service didn't go quite as well as Apple planned.
Apparently since its simultaneous release with the 2.0 firmware, the subscription-service was preventing users to send/receive emails, sync their devices, and even deleting some of the user's contacts. In response, Apple created an "apologetic" blog, stating that they have fixed over 70 bugs, however, %10 of the email lost may be gone forever.
MobileMe works by storing data and information exchanged via "cloud computing", but however, as one of the affected users said on a blog, everything had "evaporated". According to Apple's blog, the rest of the issues will be resolved within the coming days.
BBCNews: Apple blogs to disaffected users