I think it's bad, because the patent wouldn't read "Google's PageRank". It would read "A system that ranks cataloged pages by their relevance to a certain search term", which would mean every other search engine would have to license Google's tech.
Copyright already covers specific implementations. That's as far as it needs to go in software.
Well, not really. They'd only have to license it from Google if they implemented their search engine in a manner covered by Google's hypothetical patent.
Of course, apparently Google feels they have more to gain by keeping their algorithm secret than by patenting it.
Well, look at some software patents. The kind of scope and specificity in "a system that ranks cataloged pages..." is about par for the course.
Look at the patent that caused the injunction against Word ( http://www.google.com/patents/about?id=y8UkAAAAEBAJ ); it's rather vague and basically includes anything that uses or modifies XML to create a product for end-user consumption.
The enforcement depends on the judge and the parties to the suit, but it's got a really, really broad potential scope. It's not unique; most software patents are that way. You think that's a good thing?
Copyright already covers specific implementations. That's as far as it needs to go in software.