Just for my own interest i've taken a quick look at the cost of storage, using Scan's media section as my source.
All rated in my 'Pence Per Gig' ppg rating.
CD-R 100 discs (700MB) for £8.17 = 11.7 ppg
DVD-R 100 discs (of 4.7GB) for £12.33 = 2.6 ppg
DVD Dual Layer 10 discs (of 8.5GB) for £4.70 = 5.3 ppg
Blu-Ray 10 discs (of 25GB) for £29.36 = 11.8 ppg. <-- Look! Blu-Ray is as cost effective as CD!!
And for comparison, Samsung 640GB hard drive £45.70 = 7.1 ppg.
8GB USB Stick for £10.30 = 129 ppg.