Where all can the /*+ PARALLEL */ hint be used?
The Data Warehousing Guide has a chapter on parallel operations that goes over what operations can be parallelized.

You can't parallel-ize a simple CREATE TABLE statement (nor would you want to-- there wouldn't be enough work to be able to parcel it out to multiple worker threads).  You can, however, parallel-ize a CREATE TABLE AS SELECT statement either by specifying the PARALLEL hint in the SELECT or by using the PARALLEL keyword in the CREATE.