I am really waiting its more than 3 months and still there is no sign of pr updates for old sites which were also untouched in April 4 update.
It's just a guess but I reckon what they are doing is this: New pages or new sites updated a different time to older sites/pages. It could be that the datacenters can not handle doing it all in one hit. I work for a huge firm with one of the biggest databases in the southern hemisphere and they use different servers (datacenters) to update different parts of the system and also at different times. It's much more efficient this way, just on a bigger scale. It's my educated guess.
How old that site was and showed a change PR? Same here, all of my old websites did not show any PR change
Check if google did crawl your site over the last few months. If google don't even bother to come into the site, chances of an improved PR will be slim.
I think WhimperingWarrior is right. Also probably they need to be happy with the partial (new site) update before 'going global', or at least roll the results of the partial update into a 'real, complete, update'. Perhaps even sort out the spam sites problems first as well. I can't imagine why a few sites (eg jimkarter above) got updated, but I am confident the main update hasn't happened yet. Could be tomorrow, could be many months...stay calm...and read the 100's of posts here telling you why PR is unimportant (although we all secretly want higher PR)