(For example, when I mouseover the above link to his LJ I see his picture pop up like a tooltip.)
I think Greasemonkey is a minor step towards a new view of the web, where the end-user controls what they actually get from a website. The logical conclusion is to use sites as feeds (as RSS has done for most blogs for me -- I don't ever look at the author's websites). I don't think the Greasemonkey ideal will ever be integrated into a major browser because it's trivial to Greasemonkey out e.g. ads from all pages you visit. But all that means is that the power will remain in the hands of people who can take the extra step.
