There are some serious performance issues when using TimeMachine to backup your Mac over a network. In my case, an initial backup of 60 gigabytes took more than 3 days to complete.
Luckily, the problem can easily be fixed in three simple steps:
Step 1: Prevent .DS_Store file creation over network connections
Open terminal and run:
defaults write com.apple.desktopservices DSDontWriteNetworkStores true
Step 2: Fix the OS X TCP stack
/etc/sysctl.conf and add the following line:
Step 3: Reboot
After rebooting, your TimeMachine backups should run a lot faster over the network. In my case, it reduced the initial backup time from 3 days to less than 8 minutes!
So if your TimeMachine backups are slow, give it a try and let me know if it worked...