I'm not sure if this business idea is compatible with the Bitcoin transfer system:

Suppose someone starts a small business and wants people to invest in his/her idea, but the business is too small for an IPO.
This person could use Bitcoins instead of a traditional stock structure.  This person would take 100 (or any number really) of his/her
existing bitcoins and re-brand them as 100 bitcoin stocks.  Anyone interested in investing in this person's business could attempt to
buy these bitcoin stocks from the owner.  These bitcoin stocks could be purchased with normal bitcoins or with any other form of
payment.  Essentially the idea here is to allow people to take their existing bitcoins and turn them into discrete, customizable entities
which could be traded through the existing Bitcoin network.

This would require some major changes to Bitcoin.  Most importantly, a bitcoin transfer of this kind would have to contain extra
information: the stock ID associated with the transfer.  It would also be necessary to have an online reference database
where people would be able to look up information associated with this stock ID.

I was thinking about a similar thing. One can re-brand their bitcoins in existing protocol by deposit-and-immediately-withdraw'ing bitcoins to/from a announced address. So anyone who wants to handle them can track them.