There is... to some extent... but it's not exactly user friendly. If
you monitor the logs while syncing (by opening Applications >
Utilities > Console), contacts that will be changed will be listed
with one of the field names (out of potentially multiple fields) that
is causing Syncman to think that the contact has been changed.
This is good for debugging, but is obviously not meant for real-world
use. I do have plans on providing much more information within the
interface on what will be changed.