Here's a quick and dirty way to back up all of your Heroku-powered databases using their Taps gem with one easy command. It works well enough for my simple needs, but any improvements you've got would be most welcome!
Just add the following to your ~/.bash_profile, and you're good to go:

You get 1 backup free.
$ heroku bundles:capture
$ heroku bundles:download
Keep it someplace