I have worked on two sites for clients since the last update. They have both received PR4 updates (from None) in the July 2005 update. One was a site that I hand-coded from scratch so I was not too suprised with the results. The other was a knuckle buster due to a large volume of dynamic pages with lots of info in the query string. The results for the dynamic site really suprised me.
The first PR4 site didn't suprise me so much as I expected a PR3-PR4 off the bat. Well, all internal pages are PR3-4 with a few PR2's way off the homepage. I hand-coded the site and knew the quality of code going into every aspect of the site. I optimized the site using special files on the server and careful keyword measuring and placement. Using a link exchange strategy, I was only able to get a few VERY high quality links for this site over the last month and a half. I knew that even though there weren't a whole lot of links to this site, the quality would help carry it over. This site had no previous PageRank and this was it's first update.
The second site to make PR4 this time really suprised me. There are only about 5-6 static pages besides the link directory and the rest have horrible query strings after the ? in the URL. While these pages have not been updated yet by Google (if they get any), the main site and link directory (which is static) all have PR2-4. Plans are in the works to change these dynamic pages to static pages to help SERP ranking. In the meantime, I once again attribute these results to using a high quality link exchange strategy.
I have heard a lot of posts on forums in the past few days about how lots of sites went down in PR though having more links. All I can say from talking to people daily about building links and constantly evaluating links for my own directories is that many people seem to have this whole linking thing wrong. While there is no hard and fast, one-size-fits-all rules about exchanging links, but there is a lot of common sense and a few 'best practices'.
There is a lot more to think about, but starting here should put you in the ballpark. The more time you spend gaining quality links, the less of them you will need to get good results.