I'm using Dapper and there seems to be a new command format for tar. Now the --exclude statements need to go before the source directory....
Even easier...you can create a file with the words you want to exclude and use the --exclude-from=FILE. See my example below but don't copy/paste it unless you created a file called 'excludes'.
tar cvpzf backup.tgz --exclude=/proc --exclude=/lost+found --exclude=/backup.tgz --exclude=/mnt --exclude=/sys /
Hope that helps.
tar cvpzf backup.tgz --exclude_from=excludes /