For those still looking for an ORM solution, I released greenDAO some months ago. Several apps in the Android Market already use it. Unlike other Android ORM tools, one of greenDAOs primary design goals was performance. For many operations it should be multiple times faster than other solutions, e.g. it's 4-5 times faster compared to ORMLite for loading entities.
It supports relations. The documentation describes how to use relations and how you could model many-to-many relations.
Delete-cascade is a dangerous thing, and thus unsupported by greenDAO. The safer way is to delete the entities bottom-up inside a transaction.