I use MindMeister almost daily. I wanted an easy way to backup my numerous mindmaps so I crafted a Python command-line tool for this purpose. It is available through this link and works under both Windows and Linux environments. The tool performs logging in Windows registry or Linux /var/log/mm.log . For easier usage, the installer copies the command-line file to the designated python script directory.
In summary, to use the tool (assuming one as a working Python installation, 3.0 <>=2.5 ):
Step 1) Register for an API key with MindMeister
Step 2) Install the tool through the command line: easy_install jld
Step 3) Perform authorization: mm -s SECRET -k API_KEY auth
This step will open-up a browser window
Step 4) For regular backup, use a scheduler (such as Linux cron).
Suggestions are welcome!