is a technique I've used reasonably successfully when loading partitions of large tables. You have to issue the command "alter session set skip_unusable_indexes=true" before you can insert into the table. I believe this can also be done from sqlloader - there is a control file parameter SKIP_UNUSABLE_INDEXES.
The only problem is that you load into a table which has had a primary or unique key index disabled. It only works for ordinary indexes.
If you're loading a partition from scratch, the better approach is generally to load a separate table with the same structure as the partitioned table and then swap the partition with the table.