I use an old verison of Kazaa Lite.. So there is no spyware or popups. But if you get Kazaa only, its full of spyware and popups.
And I can't complain about the product itself. But finding a good clean verision of a song can take awhile, as there are some fakes that get placed on Kazaa and some people don't have a complete verision of the song on their shared directory.
So you may have to download and test a bunch of songs before you find a good verision of the song. But this mainly applies to new "Top 40" Songs.