I just ran across this same issue with the President of my company's HTC Mogul, connected via activsync directly to our Exchange server... I found that all of the contacts missing from the Mogul had content in the notes section, but so did other contacts that were not an issue. The i saw that the problem contacts' note sections all ended in numerous carriage returns (one actually only had a series of carriage returns as the note, nothing else)... I thought it was a strange coincidence, but when I removed the carriage returns and saved the contacts, each then showed up on the Mogul. Will be watching to see if this holds true going forward.