Do they? Seems they are not interested in PR for sites. If they do it should be good for seo people. 89%+ people only count seo based on google ranking only.
every search engine have their own algorithm and page rank is created by google. other search engine also have their own pageranking,but not named pagerank like alexa with alexa site info
Don't think that, Yahoo will do so. Yahoo already powered Bing for its search function. Moreover, PR is not important in terms of search result. So, actually there is no reason to work for something like ranking from Yahoo.