A friend of mine works in a body shop and he told me about this stuff too; turns out a lot of body shops are using this probably 90% of the time. It's supposed to work better than welding because it seals the panels together while bonding them. Different grades of the stuff too; ones that set up faster or slower depending on what your needs are.I didin't know about the flanging kit; sounds like a great idea. I'd been wondering about how to mount things flush (thought of using a strip of metal in behind to cover the gap that butting the new metal against old would create and then using angel hair to fill things in). I don't think I'm going to use it for anything structural like floor supports or torque boxes or anything though.
These guys have lots of good info and the forum members are pretty experienced.
http://www.autobodystore.com/cgi-bin/config.pl?index
Hope that helps,
Greg