Well, I sure wouldn't recommend a backup plan that relyed on a database export only. An export is an enhancement to a backup plan, but not a main pin. Velpuri wrote the Oracle Press Backup and Recovery books and shows various options for planning a successful backup and recovery plan. I would suggest that you look into these books for some ideas.
As an aside, I use export in my backup plans, but only for single table recovery when I don't have to worry about having the table with up to date data. If it's a static table I can restore from the previous nights export and it's faster than restoring the entire database. But then again it depends on why the database needs recovery in the first place. There is no one correct answer, it depends on your needs.