As mentioned earlier, time machine is not working out of the box on network shares as promised initially by Apple. After reading some Forums and blogs it looks like Apple stripped down Time Machine Configuration options in the final release. Never the less i managed with the help of the information provided in these forums and blogs to workaround this issue and enable Time Machine to backup to my netatalk AFP share on my Buffalo Linkstation. All you need is a spare USB disk. Here are the steps: 

  1.  connect the USB (or FW) drive to your mac
  2.  if time machine recognizes the drive just ignore it
  3. Rename the Drive to the name you would like to use for your backup share e.g. Backup
  4. Open Time Machine Configuration Dialog in System Preferences
  5. Now select your attached USB drive
  6. You will see the next backup Timer countdown, just cancel it by pressing the X button
  7. now connect your AFP share (Finder Cmd+K) 
  8. next open a terminal and copy two files from the USB Disk Volumen e.g.  
    cp /Volumes/Backup/.com.apple.timemachine.supported /Volumes/Backup-1/ 

    and 

    cp /Volumes/Backup/.00* /Volumes/Backup-1/
  9. now disconnect your USB Disk and unmount your AFP share
  10. Reconnect to your AFP share and select Backup Now by right klick (or Ctrl-Klick) on the TimeMachine Dock icon.
  11. Voila !  now your Backup should start.

you should see something like this: 
network-tm.png
Time Machine creates not a simple Directory like on the attached Disk but a sparse Image which is then automatically mounted and used as the target.

Update 1:

After hours of waiting and finally a successful backup, I found out that time machine itself does not use the created backup on the network share – so you can make an automatic backup but not use the fancy interface – which is from my point of view only about 50% of what I would like to have or in other word useless 🙁 

Update 2:

hopefully this guy is right 😉