I've been trying to get rails to work successfully with the native geometric types in postgres (point, box, etc), but out of the box rails dumbs these down to string types. This means that when rake creates my test database, it converts geometric typed columns to string types, meaning tests which utilise geometric functions blow up as they are now dealing with strings in the underlying database.
I managed to get around this with two changes in the ruby postgres adapter, and one in the active record schema_definitions file:
In postgresql_adapter.rb I added definitions for the geometric types to "native_database_types", and I uncommented the line which handles these types (interesting that it was there) in "translate_field_type".
In the active record file schema_definitions.rb I added clauses to handle these types to "simplified_type".
I don;t know if these was a better or nicer way I should have done this .....