From the user's web page activity log:

10/23/2007 03:47:58 PM - Synchronization started
Connection Info
Connection type: Dialup
Device name: WM_12345
Sync via: Sync (user initiated)
Bytes in/out: 508/418 (* actual over the air count may be higher)
Duration: 00:24

10/23/2007 03:03:49 PM - Synchronization started
Connection Info
Connection type: Dialup
Device name: WM_12345
Sync via: Sync (user initiated)
Bytes in/out: 4042/4594 (* actual over the air count may be higher)
Duration: 00:32
Wireless Email
Inbox (2 new, 5 updated, 17 deleted)
Calendar (2 new)
Tasks (no changes)
Contacts (no changes)
Notes (no changes)

The bottom entry looks normal. Inbox, etc. are updated. Top entry is when device no longer syncs. Note that there are no Inbox, Calendar, Tasks, etc.

This happens often and usually with the same, high-profile users. Anyone have clues for this one?