I don't think its too commonly used. I've got a couple just starting out, but I have found that they are unpredictable.... losing branches and/or dying unexpectedly.
There are some nice ones out there. Here are a couple of links. Walter Pall in EUrope has some very nice ones:
I have a massive trunk italica that I have had for 3 years. It is from nursery stock but the top was broken off so I got it free of charge.
The first 2 years I pruned hard to 2 leaves and wired the branches horizontally. It has responded very well and there is clear ramification results, as well as wonderful back budding on both branches and the trunk. Spring this year I put it into a restrictive bonsai pot and crossed my fingers. Great! The leaves have reduced in size much to my surprise and it is very healthy. I can now see a pleasant formal upright bonsai coming along and with its vigorous growth I can place the twigs and leaves anywhere I want.
As far as the threads from Walter P's I'm not sure if that is the same poplar that WE have here.
Mine is a White poplar (Populus alba), Walter's is a Silver, here's the WIKI that you can get online http://en.wikipedia.org/wiki/Populus_alba
you can also get info from the USDA site on Silvacs.
good luck,,
KJ