Private Betas and Private Apps will join the Public Distribution options for developers. Private Betas will not require certification but will require user registration by the developer by way of the user's Windows Live ID (limited to 100). Private Betas will have a life cycle of 90 days and should help developers iron out all the bugs before releasing the app for Public Distribution.
Private Apps will need to go through the certification process and will not be searchable in the Marketplace. Developers will distribute these apps via a deep link to allow recipients to download the app. This distribution will be well suited for enterprise/corporate applications.
Marketplace games will also require a rating and certification of those ratings if it's required by the region of distribution. This should open the door for gaming titles where concerns about mature content are present (remember Twin Blades). This would also suggest that parental controls will be present in the Marketplace as well.