I'm selling a DVD by Todd Johnson if you're interested. He (I think), started the technique. He's certainly a master of it anyway.
I had the privilege os studying with him for a couple of days last year. The technique is especially useful if you play 5 string and 6 string basses. It really cuts down on unwanted string noise, strings that you're not playing 'ringing'.
It's a more sensible way of playing. Playing while pivoting your thumb on the B string and stretching down to play the G and C strings, that's a hell of a stretch, and you're not in proper control of what you're doing.
I use a mix of 'floating thumb' and resting my thumb on the string above the one I'm playing. So my right hand moves down the strings as I play.
Check the Todd Johnson section on talkbass, there are loads of links to Youtube videos on there, showing him demonstrating the technique.