Around Chiangmai and the north, I never hear the "r" (okay, half way between an "r" and an "l") and only hear them pronounce it "kap" (or similar to that). I do hear the "r" (or whatever) more often in Bangkok and Pattaya but not all the time.
And, when listening to Thais talking, even Thais of lower class, I seem to hear it quite often. Very often when two thais are talking to each other, you'll hear the one not speaking repeatedly interjecting "kap" (or krab/krap) almost as an interjection or acknowledgment that they're still listening and/or that they agree with what's being said. Sometimes it seems to me that this is just a way of shortening a more formal "chai, kap."




