Love trello! My wife and I use it to coordinate what needs to be done around the house. And I agree with the folks at trello that email notifications (and email in general) are lousy. I don't want to see each time a card changes - the only thing I want to be alerted when a task is about to be due or is past due. Mainly so I don't get in trouble at home ;-) So I thought it would be a fun weekend project.
I use CentOS at work so I'm most comfortable with Red Hat and I've played with OpenShift, their PaaS option, before. This feels like a cron job, which OpenShift supports. Trello has a nice API so this wasn't too hard to code in Python. I didn't want to make my Trello board public of course but you can generate a token which allows read-only access to a board, once approved.
Once you get an account on OpenShift, create a python-2.6 app and add the cron cartridge:
rhc app create trellminder python-2.6
rhc cartridge add cron-1.4 -a trellminder
I use requests whenever possible - urllib2 should be avoided at all costs. To do so, add "install_requires=['requests']" to setup.py in your root dir.
There was a very helpful question on the OpenShift forum which clued me into how this script should run. Mainly, I should use a shell script to activate the Python 2.6 virtenv then call the python script. The use of a 'jobs.deny' file would force cron to call the .sh and ignore the .py.
The actual source code is posted on my github repo.