We looked into something like that when I was helping @sam with his blog package. It never took off (at least, not my pull request) so I created a shell script to do it. That way I could do backups on a cron job or run it from the command line, during a deploy script (via scp), etc.
Here’s the gist of it:
#!/bin/bash
DATE_STR=`date "+%m-%d-%y_%k-%M-%S"`;
echo "Backing up blog collectsion at $DATE_STR";
mongodump -h 127.0.0.1:3001 -d <yourDBName> -o ./$DATE_STR -c <Collection1>
mongodump -h 127.0.0.1:3001 -d <yourDBName> -o ./$DATE_STR -c <Collection2>
# Repeat for each collection you want backed up
cd $DATE_STR
tar -cf <tempFileName> meteor | gzip > <some.tar.gz filename>
In our case, this gets run before we deploy to production, for example.