The answer lies in the Smart Playlist side of iTunes, and worked on number-oriented playlists that the reader might care to consider if you need to sort out large quantities of digital music.
For a start you need a way to separate your latest acquisitions from all the other stuff in the library through an Unheard list (Smart Playlist Plays is 0) or a Recently Added list (Smart Playlist Date added in the last (say) six months Plays is less than 7, or whatever figure you specify). I like to have both, because Recently Added gives you a way to get to those recent additions after you've heard them once.
From there, I have a number of numerical Smart Playlists (named, predictably, Ones, Twos and so on) (Smart Playlist Plays is whatever number you're looking at).
That's handy when you've been doing and adding the contents of all those CDs that come on the front of magazines like Mojo to the library along with everything you've bought or downloaded.
Downloaded material, in particular, can vary markedly in sound quality and performance and those CDs on the front of magazines can contain a certain amount of material that's surplus to requirements, and unless you're in a position to give that Unheard playlist your undivided attention there's every chance things you don't really need to keep are going to slip by unnoticed.
The numbered filters make it increasingly likely you'll catch the little devils, particularly if you've checked the Controls: Shuffle By Albums option). Not sure about the contents of the CD that came with Mojo? Well, here you go. Something like William S. Burroughs doing a number called Ich Bin Von Kopf Bis Fuss Auf Liebe Eingestellt (Falling In Love Again) might slip past once, but keep the playlists for the lower numbers as low as possible and you'll catch days the little devil eventually.