Don't take passwords to your grave. Make sure others can access it all. My personal preference is to leave everything wide open but others may have different needs and views. In that case you will need a digital trustee.
Don't keep all your backups in your house. Even if you have a sprinkler system you might get hit by a meteorite or an elephant stampede or something.
REGULARLY (say monthly) move a copy somewhere else.
People propose all sorts of tedious schemes where you are supposed to go to a trusted person's house every week or month and swap hard-drives. Yeah right! How long is that program going to last? Back up online using one of the many services available.
I shoot more photos in a year than my Dad did in his life. There are more photos of my son's soccer team than were ever taken of my grandfather. (As of 2008 there are 2 billion photos on Flickr, and FIVE billion on facebook).
Until recently the challenge was to get enough data to adequately record the family history. Now we have the opposite problem, an embarassment of riches.
As of very recently, storing it is cheap. Finding something to put it in is now affordable, with home disk drives in the hundreds of gigabytes.
The challenges are managing it, and making it useful.
Modern file formats can seem enormous (video, high-resolution photos, sound recordings). Should you store these big files or compress them? It all depends what you want the file for.
For example image resolution can vary widely and so does the file size. Image resolution is often measured in ppi or pixels per inch, also called dpi, dots per inch. If you want to view images on screen, then 120ppi is fine (or even less), but print really needs 300ppi for a nice clear picture.