the best usenet nzb downloader is sabnzbd.

well i changed nzb downloaders, finally found the best one!

sabnzbd is a daemon (server) for downloading files using nzb (usenet index files, like .torrent files). it runs on windows, mac and linux. its very easy to use and has an html/web interface. it can do automatic par2 repair/filejoin, unrar/unzip and deletion of par2,rar/zip when done.

win32 / linux:
http://www.sabnzbd.org/
and for intel-mac osx binaries:
http://osx.boiboite.net/