Unfortunately, you didn't give enough information about your backup strategy to give you any concrete suggestions. Are you backing up to tape or disk? Are you using RMAN? Is the backup device local to the database server or accessed through a network?
There are a couple of things you can try. First, you can try to export in parallel to speed up backup times. RMAN handles this quite nicely. With RMAN, you can back up to multiple tape drives or disk devices at the same time. This can make a big dent in your backup window.
If your backup device is accessed through a network, consider attaching it directly to your database server. Network traffic can be your bottleneck.
Make sure that your backup device is not experiencing contention. If too many I/O operations are concurrently required of your backup device, backup operations will slow down considerably.
This was first published in August 2004