Can you back up a notebook page easily, send it instantly to someone the otherside of the planet, tag it for search and lookup on a computer, perform OCR on it in-situ, etc. ... horse for courses I say.

I agree this would be a cool thing to have, but: back up, send it out: many people have a phone that can help there (snap a photo and email it; imperfect, but often will do the job)

Also, I guess you need the OCR because flipping through pages is too slow to be useful.

Another disadvantage of this is that it you can look at only one sheet at a time. With a paper notebook, you can tear of some pages if desired.

Good points, like I said - horses for courses (the right thing where it fits in other words).

My IT teacher at school instilled the notion that we shouldn't always take a computer based approach but look at the best tech for the job, even if that is pen+paper. Sometimes a spreadsheet is the best db to use, sometimes ascii is a better image format (rarely IMO), etc..