ya know, alot of mine went from a 4 or 5 down to a zero as well..
however using:
http://www.iwebtool.com/pagerank_checker
it shows a mix of 0's and 4-5's for each of my sites..
i am guessing it's just a fluke for right now as they update PR's
especially for a few of my sites where they should have went up as I elminated outgoing links and gained a few incoming high PR links with good anchor text.. (one pr4 site that is currently 0 had nearly 1,000 outgoing links, and was changed to 0 outgoing links over 2 months ago... and google has heavily spidered the site since those changes were made).
maybe we'll have to wait a day or two to see what happens..