I have created a couple of scripts to assist in backing up the wow user interface and syncing with other machines. They can be downloaded here.
To get it working extract zip file into you Dropbox folder.
The zip contains 3 folders. (Backup: Contains your backed up files. Scripts : for reference. Applications : The compiled scripts. )
Run the backup application in the applications folder. This will copy your interface and WTF folders into your Dropbox backup folder.
To restore your interface on this machine or another just run the restore application in the application folder. WARNING : This will delete your existing interface and WTF folders in your wow directory. You will be warned prior to this. Please backup your WTF and interface folder prior to running this in case you need to restore your old files.