I can tell the difference between VBR mp3 224-320 ripped at highest quality and CD, but tbh the difference is quite negligible. MP3 does me fine for general listening, although I would much rather have a CD if i'm paying money... mp3 albums I only pay for if it's like 50p-£1 for an album, and i'd rather just nab it free. If I like it, buying the CD seems a lot more appealing generally, or at least buying something off the artists website to fill up the coffers a bit.
I think music is going to move to the direction of artists selling it through their websites or smaller record label websites, and you'll get a greater choice of what you download and how much you pay for it. I know Nine Inch Nails did that at some point; you could choose between the studio files, .WAV and high quality .mp3, and you paid in relation to this. Good idea IMO, everyone's fed up with the artist-fucking, overpriced, technology-fearing record labels...