Looks like the other create functions in nova-manage doesn't check for existing entries, too. Please check all create functions.

# nova-manage project create testing admin
2011-02-06 21:50:21,181 ERROR nova.exception [-] DB exception wrapped
(nova.exception): TRACE: Traceback (most recent call last):
(nova.exception): TRACE:   File "/usr/lib64/python2.6/site-packages/nova/exception.py", line 105, in _wrap
(nova.exception): TRACE:     return f(*args, **kwargs)
(nova.exception): TRACE:   File "/usr/lib64/python2.6/site-packages/sqlalchemy/orm/session.py", line 1397, in flush
(nova.exception): TRACE:     self._flush(objects)
(nova.exception): TRACE:   File "/usr/lib64/python2.6/site-packages/sqlalchemy/orm/session.py", line 1478, in _flush
(nova.exception): TRACE:     flush_context.execute()
(nova.exception): TRACE:   File "/usr/lib64/python2.6/site-packages/sqlalchemy/orm/unitofwork.py", line 304, in execute
(nova.exception): TRACE:     rec.execute(self)
(nova.exception): TRACE:   File "/usr/lib64/python2.6/site-packages/sqlalchemy/orm/unitofwork.py", line 448, in execute
(nova.exception): TRACE:     uow
(nova.exception): TRACE:   File "/usr/lib64/python2.6/site-packages/sqlalchemy/orm/mapper.py", line 1872, in _save_obj
(nova.exception): TRACE:     execute(statement, params)
(nova.exception): TRACE:   File "/usr/lib64/python2.6/site-packages/sqlalchemy/engine/base.py", line 1191, in execute
(nova.exception): TRACE:     params)
(nova.exception): TRACE:   File "/usr/lib64/python2.6/site-packages/sqlalchemy/engine/base.py", line 1271, in _execute_clauseelement
(nova.exception): TRACE:     return self.__execute_context(context)
(nova.exception): TRACE:   File "/usr/lib64/python2.6/site-packages/sqlalchemy/engine/base.py", line 1302, in __execute_context
(nova.exception): TRACE:     context.parameters[0], context=context)
(nova.exception): TRACE:   File "/usr/lib64/python2.6/site-packages/sqlalchemy/engine/base.py", line 1401, in _cursor_execute
(nova.exception): TRACE:     context)
(nova.exception): TRACE:   File "/usr/lib64/python2.6/site-packages/sqlalchemy/engine/base.py", line 1394, in _cursor_execute
(nova.exception): TRACE:     context)
(nova.exception): TRACE:   File "/usr/lib64/python2.6/site-packages/sqlalchemy/engine/default.py", line 299, in do_execute
(nova.exception): TRACE:     cursor.execute(statement, parameters)
(nova.exception): TRACE:   File "/usr/lib64/python2.6/site-packages/MySQLdb/cursors.py", line 166, in execute
(nova.exception): TRACE:     self.errorhandler(self, exc, value)
(nova.exception): TRACE:   File "/usr/lib64/python2.6/site-packages/MySQLdb/connections.py", line 35, in defaulterrorhandler
(nova.exception): TRACE:     raise errorclass, errorvalue
(nova.exception): TRACE: IntegrityError: (IntegrityError) (1062, "Duplicate entry 'testing' for key 1") 'INSERT INTO projects (created_at, updated_at, deleted_at, deleted, id, name, description, project_manager) VALUES (%s, %s, %s, %s, %s, %s, %s, %s)' (datetime.datetime(2011, 2, 6, 20, 50, 21, 180352), None, None, False, 'testing', 'testing', 'testing', 'admin')
(nova.exception): TRACE: 
2011-02-06 21:50:21,186 CRITICAL nova.root [-] (IntegrityError) (1062, "Duplicate entry 'testing' for key 1") 'INSERT INTO projects (created_at, updated_at, deleted_at, deleted, id, name, description, project_manager) VALUES (%s, %s, %s, %s, %s, %s, %s, %s)' (datetime.datetime(2011, 2, 6, 20, 50, 21, 180352), None, None, False, 'testing', 'testing', 'testing', 'admin')
(nova.root): TRACE: Traceback (most recent call last):
(nova.root): TRACE:   File "/usr/bin/nova-manage", line 694, in <module>
(nova.root): TRACE:     main()
(nova.root): TRACE:   File "/usr/bin/nova-manage", line 686, in main
(nova.root): TRACE:     fn(*argv)
(nova.root): TRACE:   File "/usr/bin/nova-manage", line 364, in create
(nova.root): TRACE:     self.manager.create_project(name, project_manager, description)
(nova.root): TRACE:   File "/usr/lib64/python2.6/site-packages/nova/auth/manager.py", line 513, in create_project
(nova.root): TRACE:     member_users)
(nova.root): TRACE:   File "/usr/lib64/python2.6/site-packages/nova/auth/dbdriver.py", line 133, in create_project
(nova.root): TRACE:     project = db.project_create(context.get_admin_context(), values)
(nova.root): TRACE:   File "/usr/lib64/python2.6/site-packages/nova/db/api.py", line 887, in project_create
(nova.root): TRACE:     return IMPL.project_create(context, values)
(nova.root): TRACE:   File "/usr/lib64/python2.6/site-packages/nova/db/sqlalchemy/api.py", line 1759, in project_create
(nova.root): TRACE:     project_ref.save()
(nova.root): TRACE:   File "/usr/lib64/python2.6/site-packages/nova/db/sqlalchemy/models.py", line 57, in save
(nova.root): TRACE:     session.flush()
(nova.root): TRACE:   File "/usr/lib64/python2.6/site-packages/nova/exception.py", line 108, in _wrap
(nova.root): TRACE:     raise DBError(e)
(nova.root): TRACE: DBError: (IntegrityError) (1062, "Duplicate entry 'testing' for key 1") 'INSERT INTO projects (created_at, updated_at, deleted_at, deleted, id, name, description, project_manager) VALUES (%s, %s, %s, %s, %s, %s, %s, %s)' (datetime.datetime(2011, 2, 6, 20, 50, 21, 180352), None, None, False, 'testing', 'testing', 'testing', 'admin')
(nova.root): TRACE: