Was watching 'DOWNLOAD: THE TRUE STORY OF THE INTERNET : Search Wars' today and couldn't help but realize that most innovations that have come out on the web and become BIG have been simple ideas.
I mean it's not earth shattering to want a give users better searches. Just as it is not earth shattering to rank sites higher which have more recommendations (in bound links). Also it is not something out of this world to match keywords with relevant advertisements.
I think the same would apply to most of the internet innovations. I mean it's easy to see how people would love to upload and share videos or even just want to watch random ones. It's easy to see how people would like to upload pictures and share them. It's easy to see how people would like to have online diaries etc.
It's just a matter of being sure that you have something that offers value to others and that it can be a money churning machine. And with advertisers moving more and more advertising revenue to the internet, I think worry about revenues is secondary if you have advertising avenues on your invention.