This guide is intended for Ubuntu users (it may work on other Linux distro though).
If you are running TOMBOY 0.15.6 or later, all your TOMBOY notes are stored on ~/.local/share/tomboy/. You can change its default directory for your notes. This especially makes sense if you dual boot Ubuntu for example with Windows so you only want the same notes accessible from both OSs.
Open terminal then run these commands:
1. sudo cp /etc/profile /etc/profile.bak
(make backup of /etc/profile into /etc/profile.bak)
2. sudo gedit /etc/profile
3. copy and paste this line (without quotes): "export TOMBOY_PATH=/media/STORAGE/Tomboy_notes". This will set up "/media/STORAGE/Tomboy_notes" for your Tomboy PATH. Change "/media/STORAGE/Tomboy_notes" accordingly to what directory you want to store your notes.
4. Restart the system and now Tomboy will read notes stored in that directory.