Wolfram Alpha Search Engine:
http://www.wolframalpha.com/Wow! it's like seeing information EXACTLY IN THE WAY I AM USED TO STORING IT IN MY BRAIN. I didn't even realise how I remember and organise the information in my brain it up to now. It is as if I was looking at a snapshot, a photo of my memory. Awesome :) and this makes it so usable, so easy to navigate...
The only problem is that it does not understand more complicated questions, e.g. "what is a white hole" gave information about white colour... i guess it is still a long way to go before it can actually be useful..
..but anyway I just really understood the power of Semantic Web :)