About 7 or 8 years ago I ripped all our CDs to MP3 and stuck all the music on a house media server.
I used what was, at the time, a good MP3 encoder: LAME, with the –r3mix preset that had been tweaked by the members of an online forum for MP3 enthusiasts.
MP3 encoder quality has made some strong progress since then, and disk space has become even less of an issue. Accordingly, I’m re-encoding my favorite stuff using the latest copy of LAME and –preset standard –vbr-new. Even on my office Cambridge Soundworks speakers, the difference is noticeable. I figure this will be the last time I do this, in a couple of years I’ll just rip everything lossless.
iTunes also got much better at encoding with version 7. So if you ripped your favorite album to MP3 some years ago, it might be worth re-doing it and giving yourself a free audio upgrade.
(To my ears, LAME encodings still sound better than iTunes, but iTunes 7 is way better than earlier versions. That said, there’s a free friendly Mac audio ripper/encoder front end called Max that will call LAME for the encoding.)