You should probably all be aware that Nefario is already planning on creating a legal, regulated Bitcoin stock exchange service (of some sort) once this blows over.
I don't mean to be a hater, but I think that's going to be a pretty hard road to go down. Stock exchanges are complicated financial services, perhaps best left to professionals, no?
Another interesting thing from the conference though was talk about the Bitcoin Scripting which could allow for exchanges to operate without any 3rd party. Companies could run the process themselves, or someone could develop software allowing people to run an exchange themselves.
Thats what I was thinking, kinda like trading ecrypted certificates. Make a place where you can post the sale of these certificates and then leave paying dividends to the issuer. Make some kind of rating system, where people who have bought sold like silk road can rate the sellers and the product.