THIS is as good a tutorial for The Nashville Number System as you're going to find. It does NOT replace standard notation, but IF you're working inside a particular style (of course, this came along in the days of 1-4-5 country tunes when 3 hour sessions frequently resulted in three or four finished tunes and guys had to work fast) and everyone's on the same page, you can really make time with this. I've used and seen it a lot, and the best thing about it (particularly with 5 or 6 string basses where transposing is so easy) is that it utterly breaks you of thinking in terms of playing often in the same key(s) and you automatically get a better ear for the intervals, 1-4, 2-6, whatever comes along.