In case you Mac TimeMachine Takes long ... After Mountain Lion the backup takes long ... I think there is a bug in spotlight.
How to solve it ?
Technically stop the spotlight using the command ...
Open up a terminal
> sudo launchctl unload -w /System/Library/LaunchDaemons/com.apple.metadata.mds.plist
Now the Backup will be faster.
Once done enable the spotlight back
> sudo launchctl load -w /System/Library/LaunchDaemons/com.apple.metadata.mds.plist
My backup took very long ... got this solution and finished my back up.
Hope this helps ...