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.
This is an incompetent design. The responsible engineer and product managers should hand their head in shame.