Blue-Ray Disc are good back-up media @ 25G or 50G. Thats what i use to save my system image files. Few disc needed instead of multiple DVD.
I save recorded HDTV Shows/Movies and Blue Ray disc come in handy. Also i save multiple DVD-movies on a single Blue-Ray Disc.
My LG Blue-Ray/HD-DVD Player Blue-Ray/DVD Writer is one of the most reliable optical drive i have. I only use one optical drive in my system. Optical drives are under-utilized for most part.
Blue Ray writer is ~ $199.99 to date. Blue Ray player is almost half the price.
Use the money somewhere else if you are not sure of what you need.