I really like the ability to share documents via the cloud but we have issues using it in our company. People who we share with don't see the "guest option" and refuse to get an adobe account and thus don't comment or request we share the original with them. Thus we have had problems with adoption and had to revert to sharing through mail. I think you have tried to make people get an account unknowingly this is discouraging adoption across a wider audience. I suggest a quick fix with the visual design to make sure that both options are treated equally.