I don't fully trust Optical, although when I've had to go to old archives (DVDs burnt 5 years ago) I've not had a problem recovering files.
I don't fully trust Hard Drives - had too many go kaput on me, although quite often it's the power supply and not the drive.
I certainly don't trust tape drives - http://en.wikipedia.org/wiki/Tape_drive#Reliability
We backup about 400GB of data to tape each night at work and have a legal requirement to keep one set of tapes each month for at least 7 years. We've had problems restoring from tape before - and our tapes are kept off-site in a specialist storage facility i.e. correct temperature and humidity - and had to rely on specialist data recovery firms. This is for financial data at work rather then photographs at home.
I think the moral of the story is never to trust your data source - be it the backup or
the original. Therefore you need to have multiple copies of your data on multiple media types stored in multiple locations. Data failure wil
l happen to you and the countdown clock for your personal disaster is already ticking.