I own Newsbin Pro and felt the same way as you until I discovered Hellanzb. This a Unix app which is only a bit involved to set up the first time and then it does it ALL! It runs in the terminal but there is a widget to GUify it in Dashboard if you like.
Here's an awesome step by step guide if you're interested:
http://www.macbookfan.eu/2006/07/11/howto-nzb-par-and-unrar-all-in-one-for-osx/
The best part of this setup (besides being totally free) is it is FAST as lightning, supports as many pipes and servers that you can throw at it AND it not only processes the NZB files it downloads only as many PARs as necessary for posts with errors and then fixes them and unRARs everything all in the background. Then it deletes all the working files for you leaving only the finished product.
Its really amazing and I haven't used Newsbin Pro in a few months. Originally NBPro was my main reason for running Parallels.
Last edited: Nov 27, 2006