Every few weeks, I run across an Apple bug so egregious that I can only conclude nobody there cares.
The MobileMe contact sync bug is one of those. As best I can tell only the first, last and perhaps company strings are used to match contacts when synchronizing. So if a contact has only an email address, then the match is on an empty string (null key). This produces many-to-many combinatorials, email addresses that grow with each sync until every empty name contact has every other empty name email.