And in any case, no one actually reads software patents (lawyers tell you not to!), so even if it was patented but not published or otherwise documented, no one would have known about it.
While the PageRank patent is definitely not a trivial patent - unlike the vast majority of software patents - it still isn't an example of a patent used for good.
Google has been a huge net positive in the development of the Internet in the last decade+. All of this development is the result of Google's dominance in search. The PageRank algorithm was where that began. Yes, things might have turned out the same without the patent. Or maybe Yahoo would have integrated the algorithm and cut Google off at its knees, and we'd all be stuck using hotmail with 2MB inboxes. I think it's unfair to simply dismiss the beneficial impact of the patent on the algorithm that started Google.
What do you mean by good, then? It has generated lots of cash for Google and thus provided lots of jobs.
Unless you believe that it was Google patent on page rank algorithm that prevented all other companies to get better at doing search.
To this, the only major point of consideration should be: Without patent protection, would this technology have been developed anyways?
For the vast majority of patented software, the answer is yes. Probably including pagerank and mp3. The patent process brings no value to society and therefore shouldn't be enforced by society.
In the case of drug discovery & development, the answer clearly different. Patents make sense.