I have been on a bit of a mission to get my Apple MacBook Pro to backup to my Ubuntu Server using the Time Machine.app. After alot of research turns out it was to much hassle for my liking.
You can enable Mac’s Time Machine.app to see unorthodox network and external drives by typing to following into the terminal.
defaults write com.apple.systempreferences TMShowUnsupportedNetworkVolumes 1
Time Machine.app could then see the samba shared network drive but could not backup to it correctly due to Ubuntu not supporting AFP (Apple Filing Protocol).
There is a way to get AFP working with Ubuntu therefore theoretically allowing Time Machine.app backup to a Ubuntu server, sadly it was to much effort.
Instead i would suggest using CrashPlan, i will post a tutorial soon.