If you're coming from CM07 and CM12 is new to you, you'll notice that certain site roles have been removed.  No need to panic, doesn't mean that functionality was removed.  Below is what has been removed for CM12:

• PXE service point.  This is now part of a distribution point.
• Reporting point.  Reporting services point is used with SRS.
• Server locator point.  This is now part of the management point.  That means no more "SMSSLP=" in the client install properties.
• Branch distribution point.  A standard distribution point supports workstations or servers that are members of a domain.  The functionality of the branch distribution point is now a BranchCache setting for an application deployment type and the package deployment.

New site roles in CM12:

• Application Catalog website point and Application Catalog web services point.  Both of these roles require IIS and support Software Center which is a new app on the client side.
• Enrollment proxy point.  Manages enrollment requests for mobile devices.  This role also requires IIS.

You can no longer use NLB for management points, not supported.  CM12 will perform this functionality automatically when multiple management points exist in the site.

The idea of a "default" management  point at a primary site is no more.  You can now install multiple management points and clients will automatically select one.  This functionality allows CM12 to scale and support more clients in a single site and also provides redundancy.  Prior to CM12, you'd need to use a NLB cluster for the MPs to obtain redundancy.  Again, this is no longer supported in CM12.

There are more changes but this is what I was able to note down at MMS.  I will update this post as needed.