There is a thread at Search Engine Watch Forums named Future PR Fact or Fantasy??? One of the questions asked by the member was;
Many tools on the web claim to "predict" a site's future PR can this actually be done, is the info they provide true.Also I see that the info one tool provides contradicts that provided by another tool, which one do i trust.
I believe I was one of the first, if not the first, to come up with the Google PageRank Prediction Tool. I launched that tool on April 1st, 2005 - yes it was April fools day. To appease the SEM community, I added a line about the tool should be used for "entertainment purposes only." How do I come up with the future PR? I pull some historical data from different places, I won't say exactly what they are, and I either increase the current PageRank value of a page and or decrease it by a percentage factor.
So is it accurate? No way! It was an April fools joke. Sometimes it is right, and often it is wrong. But I still get emails, at least once per week, asking me questions about the tool or ways to help increase people's pagerank.
There are other tools that look at your PageRank at all the Google datacenters. They are not really future pagerank tools, they check your real time pagerank at these datacenters. If a "Google Dance" or PageRank update is taking place, it will show the current pagerank at that datacenter.
Forum discussion at Search Engine Watch Forums.