I think it would be a great idea to put a compact flash card input on a receiver. That way, you could download music straight from your PC, and put it in the receiver. This would mean less input/output resulting in less quality.(ie:wouldnt have to run through a cdplayer)
Many tv's are starting to have memory input--like Memory Stick on Sony's and various other types on other brands. But this is mostly for photo's, slides, etc.
The main problem with your proposal is that most people have already compressed into MP3 format the sound onto a computer or MP3 player. Most of the audio damage has been done. As audio doesn't require the big bandwidth of video I am sure a USB input won't have an audible effect. And lots of people have hard drives and MP3's that can hook-up via USB and with firewire and USB on many IPODS.
Gregory: my projector takes a memory stick. Suppose to be for "presentations". I don't think I'll ever use this function.
Anyhow, it's interesting what the poster has written. Taken at first glance, I can easily see some opportunistic company (Sony) adding this to their receivers as a marketing gimmick. As you wrote Gregory, I high-bandwidth connection would be better... like USB or IEE-1394 (FireWire).
My H/K can decode MP3, but I've yet to even IMAGINE doing anything with this. I plan to build a new Audio Visual electronics system which will include a Digital Media PC (probably Gateway's).
Suppose to be for "presentations". I don't think I'll ever use this function.