I can't remember the last time I bought an audio CD. There's not much new music worth listening to, and the odd track I like I'll download illegally - I feel I've given the music industry enough of my cash already over the years. And anyway, if you buy an audio CD these days it'll most likely be a non-standard, copy-protected disc (or try and install some crap software on your PC).
I can very easily tell the difference between mp3 and uncompressed WAV. Especially with orchestral music. I don't know how to describe it... cycling? Wahwahwah.... It's very obvious.
I often see posts on here from people who claim they can hear the difference between audio encoded with lossy compression and the uncompressed original. Personally I'm "agnostic" - I believe that some people genuinely can hear a difference. However, I also believe in the "placebo effect" (because I've experienced it myself); this is where you perceive a loss in quality because you know what you're listening to is compressed. For this reason, unless someone can support their claim with ABX test results, I will always regard such statements as subjective opinion.