I just recently updated my macbook pro to Mountain Lion. I use rsync to make backups of certain directories on my macbook pro my timecapsule wireless router with build-in harddisk.
rsync -avzm --delete --exclude-from '/some_dir/exclude_list.txt' \ /Volumes/Data/some_other_dir /Volumes/TimeCapsule/some_other_dir/ \ 2>> ~/tmp/sync_error.txt
Before Mountain Lion everything worked fine. Rsync only copied new or changed files. Now, after the upgrade, rsync wants to copy all files every time, over and over again. Even if they did not change or were not deleted on the remote host (timecapsule). I don't know why (I do not encounter any errors during the rsync).