Could you please add a feature for boost to automatically create a CACHE.TAG text file in the caches directory? CACHE.TAG is a simple specification for applications to mark cache directories so that they don't need to be backed up. Details are here: http://www.brynosaurus.com/cachedir/ and here is the typical contents:

Signature: 8a477f597d28d172789f06886806bc55
# This file is a cache directory tag created by (application name).
# For information about cache directory tags, see:
# http://www.brynosaurus.com/cachedir/

I use a cron job to backup my production file directory nightly using tar (backup and migrate was hanging on my 70,000 node database). tar used to fail because a cache file would be different before and after reading. I fixed that issue with the ignore-failed-read flag, but exclude-caches works even better, because the archives are so much smaller. exclude-caches looks for a CACHE.TAG text file in the caches directory. Of course, I create it manually, but other users would probably find it useful to have it there automatically. Also, it would be nice if it were auto-regenerated if I "rm -rf caches/*". Here is the cron entry I now use:

/bin/tar -cpz --exclude-caches --ignore-failed-read --file=/var/backups/drupal/files_`date +'\%Y\%m\%d_\%H\%M\%S'`.tgz -C /var/www/autism.healingthresholds.com .

Finally, I found the excluding the caches directory very helpful when I want to copy the production file directory to a dev installation. Rather than having to copy everything (which takes a while) and then delete the caches folder, I can do this:

sudo /bin/tar -cp --exclude-caches -C /var/www/autism.healingthresholds.com . | sudo /bin/tar -x --owner=www-data -C /var/www/dev.healingthresholds.com

This copies everything except for the caches directory, and so is much faster.

Thanks so much for supporting boost, which is just awesome.