The release notes state...
which in turn reveals...
This SDK release provides the same developer tools as the Android 1.5 SDK, Release 1, but provides an updated Android 1.5 system image that includes a security patch for the issue described in the oCert advisory below:
Interesting... also the probable cause of the Cupcake update delays perhaps?
Android, an open source mobile phone platform, improperly checks developer certificates when installing packages that request the shared user identifier (uid) permission.
Normally, Android applications will be allowed to share a uid if the packages are all signed by the same developer certificate and request permission to do so at install-time. This allows for packages from the same author to share data. Without enforcement of that behavior, it is possible for any application to be installed in such a manner that it gains access to another (existing) application's data.