72,000 songs...all 192 bit rate, since I'm a dj and do sound system installations for a living(Purdue Football stadium, Basilica at Notre Dame, Excalibur Nightclub Chicago.. and many more) I can tell you the lesser bit rate mp3's really sound terrible on a large sound system, so for iPods, or anything you listen to with a headphone I'd say 128 is fine but If your a dj, do weddings nightclubs or other I'd go with a higher rate...You can see major differences in what it sounds like when you look at what the eq microphone hears back...(this is how we EQ a room)also keep in mind distortion is what blows a speaker not the power, lesser bit rates have more distortion, also one thing I have noticed for those of you who actually mix there music, is the lessor bit rates dont seem to keep the beats per minute consistent, so if I'm cueing up a song to mix and its 125 beats per minute, it may be ok for 7-8 beats then its off to 123 bpm and back up to 129bpm, it makes it much harder to mix with..the higher bit rates seem to hold the time better, fortunately for me I have a KEY lock on my mixer...the idea of the bit rate is its compressing the sound(removing data, or changing it)the lessor the bit rate the more missing data from the original recording, in a perfect world we would have gigs and gigs of storage space and all our mp3's would be 320 bit