The new way pagerank is calculated differs in the following way.
Pre July 09 - if you had a page that was PageRank 4 and the page had 10 outbound links on it and you no-followed 5 of the links, but left 5 links for google to follow... google would divide 100% of the pages PageRank (PR4) between the 5 links without the no-follow and give 100% of the
PR to the pages without the no-follow. Of course google would not give any pagerank to the links with no-follow.
After July 09, the algo has been tweaked so that in the same scenario as above, the five links without the no-follow will now only get 50% of the total PageRank of the page (PR2) that will be divided between the five out bound links, instead of the 100% of the Pagerank (PR4) as before.
The pagerank that is not passed does not actually disappear or evaporate, the
PR is still carried by the original page/site, however you are not going to increase the Pagerank that is passed by the links by having all but a couple of links on a page no-followed.
Google did this in an effort to stop what some
SEO's call "PageRank Sculpting". "PageRank Sculpting" = effort to artificially increase the pagerank that is passed by a link.
FYI - googlebot still follows the no-follow and indexes the no follow pages, it just does not transfer any pagerank to them.
NOTE: We have recently noticed that Google seems to be reducing the 'Trust Rank' of sites that extensively use no-follow is an effort to "pageRank Sculpt".
If you have been using the no-follow to sculpt pagerank... we suggest you reevaluate your strategy.