I have a week day nightly incremental backup that compliments my once a week full backup but even when I know very few files have not been modified since the last incremental or full backup, a substantial amount is always backed up! It seems to be always around 700 MB. Before you jump the conclusion it is my mailbox's I do exclude my exchange MDB data, here is the command and arguments:
START ntbackup backup "@C:\Backup Scripts\FullBackupSelection.bks" /F "G:\IncrementalBackup1.bkf" /FU /V:no /R:no /L:s /M incremental
C:\ C:\Program Files\Exchsrvr\MDBDATA\ /Exclude D:\ D:\Exchsvr\ /Exclude SystemState
I am running MS Server 2003 for Small Business Server SP2.