I think that in the real world, 120GB is plenty. I have spent the last three days loading up around 150 CDs which I have not played in a while for a total of around 35GB. I was surprised to hear a significant audio improvement over the Shuffle I have been using...until I realised that I had ripped the whole lot to wav with no compression. A small change in this department now will probably mean that I don't have sufficient silvers to fill the device

(No point in multiple copies of Bowie now is there?)
But surely the 160 GB is better than the 120GB if you want your music in WAV or Apple lossless and a few videos / DVD's on your ipod as well, ie at the same time. I was reading a review the other day on the new 120GB, and Which magazine reckons the new 120Gb has a lot better sound capability than the old 80 & 160Gb models, but to take advantage of it it says you must encode at higher than the default 128kbs and of course use decent ear / head phones and not the supplied Apple ones.
They concluded that for music buffs the 120Gb clasic is the one to have because of the sound quality and HD space and the ipod touch is the one to have if you are into everything ie music ( compressed at 128kbs I assume to to small capacity GB's ) vids, internet and games etc.
You pays yer money and take yer choice I suppose, but I would still prefer the 160Gb Classic simply because it has more GB's and thus more options available regarding a music and video mix.
It seems a strange decision to sell a less GB version even if it does have ( slightly ) superior sound over the older 160GB version.