Don't Run Two Backup Jobs At Once !!!
I just configured my Dirvish to do nightly backups but check that the previous night's backup has finished. If the previous night's backup is still running, it doesn't start a fresh backup job.
I did this because I was backing up a machine with a lot of files sitting behind a tragically slow-uplink cable modem.
http://svn.asheesh.org/svn/public/code/dirvish_pre_post_server/ has a README and the code. Let me (Asheesh Laroia <asheesh@asheesh.org>) know if there's any problem with this!