One subject that fascinates me (and probably me alone I suspect, being a huge geek) is the direction the internet is going in.
I find it amazing that this thing, entity, whatever you want to call it has grown from a small network of relatively simple computers which were born out of a wish to share information between scientists. Facebook alone now states that its users create more than 25 Billion pieces of content each month, and that's just facebook, imagine what that figure is for all sites globally.