There doesn't need to be consideration in this case because there is detrimental reliance sufficient to establish promissory estoppel (see my other post). But there was consideration -- Goat acquired shares on GLBSE, transactions for which GLBSE receives a commission.
You'd need a lawyer with
huge balls to argue that this counts as consideration.
A peppercorn doesn't cease to be good consideration should it become known the payee doesn't like pepper and has thrown away the corn.