Hi
As far as I know, there is no impact on performance (noticeable) on which order you have your columns.
However, a good rule of thumb, is to have the primary key columns in the table as the first columns. (These are least likely to be updated as well)
What causes performance impact, is repeated updates on a row after having added more rows (potentially to the same block, filling it), since you will then experience chained rows (Do an analyze on the table to see the chain count in selecting from USER_TABLES)