If you're deploying your apps on Heroku, AppFog or other PaaS provider, you're probably keeping your MongoDB data on MongoLab or MongoHQ.
Here's a short shell script to do a local, compressed and timestamped backup of a MongoLab database:
echo "\n\n\nDownloading database...\n\n\n"
mongodump -h dsXXXXXX.mongolab.com:XXXXX \
-d database_name \
-u user_name \
-p secret_password \
echo "\n\n\nArchiving temporary backup folder...\n\n\n"
zip -r ./backup/mongolab-$(date +"%Y%m%d-%H%M%S").zip ./backup/mongolab
echo "\n\n\nDeleting temporary backup folder..."
rm -R ./backup/mongolab