"How many years?"
I've thought about that a lot.
It wasn't that long ago that those memos on Bush's National Guard service would never have been seen outside the news organization, other than being quoted in newspapers. Heck, if CBS had not been inspired to actually put images of the memos on the Web, we would never have known.
Given this and a number of other web-related things that happened in 2004, I would confidently say that if there was no internet, Kerry would be president today. You can look on that as good or bad, but it's still true.