Hard drives get bigger and cheaper

I recently upgraded my old removable IDE caddy with a 500GB hard drive for about £60 and upgraded an old USB HD brick to 500GB in the same way. (In case you're wondering, I've put 350GB of data on them both already, they're my dual independent data store). If I ever get round to fitting an e-SATA adapter to my PC backplate there's a 1TB SATA drive for £97 retail at Saverstore.

If I was buying in bulk from the HD manufacturers, they'd be even cheaper than that and they'll be cheaper still in the future. I can't imagine using optical or tape even for archival backup since HD is so easy to connect into a PC, so easy to buy, only two standards - both well supported (IDE and SATA) and the standard is transparent to OS and application software. It's also fast/random access if you need that.