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
will happen to you and the countdown clock for your personal disaster is already ticking.
Ian