I haven't had much time to explore Kazaa, but my first impression is that the Web-based service is miles behind the competition. It's as if the company locked its technologists in a room four years ago and they've just now emerged, having missed the growth of social networks, the explosion in smartphone usage and the death of music DRM. The service costs $15 a month -- 50% more than Rdio, MOG or Rhapsody -- and doesn't have a mobile app. Instead, it offers unlimited streams and tethered downloads (that is, songs wrapped in electronic locks to deter copying) that can be played only by Kazaa's proprietary plugin for Windows Media Player.

It also has only rudimentary social-media features, most notably the ability to play other users' playlists and to watch a continuously updated list of what other users are playing. And although there are a handful of "editor's picks," there's no preference engine to recommend tracks based on a user's tastes -- a major handicap when it comes to discovering music. Essentially, users are left to search for tracks or artists they already know, or take unguided tours through the library's eight genres.