Very low from the synchronization perspective (MWI status, etc.)
In the past week, my Unity server with 300 subscribers has sent only 1.7 MB of data between itself and the Domino servers to keep MWI's in sync, read/unread, etc.
The real traffic comes from Voice Mail messages, which are .WAV files, uncompressed u-law codec. Those typically range from 200KB to 500 KB each in my environment.
