It takes a while for the junk filter to 'learn' what's junk & what's not. Sometimes you'll have to mark files 'not junk' if they've been wrongly marked as junk.

If you want to keep using it, there's a lot of info here
http://www.gnutellaforums.com/showth...ht=junk+filter

You can always filter out certain words (sponsored, iPod, buylegalmp3 etc) using the keyword filter in tools > options.