For me it would be a problem because we have no way of judging the importance, traffic or influence of page/site.
John Scott is right that inbound links are a good measure, but PR
is only a reflection of that. If PR
disappears we will turn to other measures like pure inbound links (without knowing if those links themselves come from important sites). The problem is that Google have disabled link discovery too, which is why John says he uses Yahoo. The problem is that Yahoo sucks in all types of links (including nofollow, I am right?).
We can't use SERPs because each search phrase returns different results and there are trillions of search combinations. Because a site is #1 for the term "sony handycam with green beans" I learn nothing.
The bottom line is that Google will leave us high and dry in terms of understanding how THEY think about our sites.
What will happen is that Google will be saying, "hey, this is our search engine and what you see is what you get, like it or lump it." Now they are allowed to say that but that isn't how they started in the search business, THEY started the whole pagerank thing, not us, THEY published the algorithms, THEY created the monster. Now THEY have to be responsible and live with it.
Google have a social contract with us (I don't know if social contract is the right term but I can't think of a better one right now, may be understanding or agreement would be better). Google became popular because the page rank algorithm works. They can't just break that agreement/understanding with us now.
Creating a system, watching the world follow that system, watching a whole economy grow from that system and then shut it all down, isn't in line with "do no evil."