Silicon-bronze is great in non-structural welds. You shouldn't be really melting the parent material when using it. It's good for fillet welds and lap welds. I have heard of problems with body fillers not sticking but that could have been some misidentified brazing. I like to use it to fill in areas that will be powdercoated. It can also be used around header flanges to add some strength to the joint. Mig welding with it always seemed to produce an ugly weld. Oh and it's expensive!
This is Ron Covell's take on the subject.
http://metalshapers.org/101/covell/c...ilbronze.shtml