Probably the single most important difference between disk & tape backup is the time to restore.  Tape backups take "forever" compared to a restore from disk - and that's if you just happen to have the tape available onsite - worst case you might be looking at several hours to get the tape back onsite before you can even begin your restore.

I typically advocate a dump & sweep approach to database backups with a nominal retention on disk and longer term retention on tape.  Reality is that most database backups are useless beyond a couple of days - would you want to have to tell the business that they have to redo several days of transactions?  Me neither.

The biggest problem with most "enterprise" backup systems like Veritas is that they are only capable of taking backups of the database each night (if you're lucky) and frequently only able to take a full backup of "everything" over the weekend which is just fine if you're backing up a database that is only updated once a month but just doesn't cut it when you need to be able to recover to within a shorter timeframe (e.g. 10 minutes). 

Joe