In my opinions, the changes are unreasonable, cos' I've noticed a lot of new sites (less than a year) of mine jump from pr0 to pr2-3 without any serious link building, however, many other webmasters have aged domains with high quality backlinks and most of all, have good content on them, their pr decrease at least 1-2, so? I don't think that's reasonable changes, Ithink google has already changed its way in view of calculating pagerank, and we all have to keep it with it.....i'm happy with the change though
IMHO, I really think this was a major update as: 1- Backlinks Updated 2- PageRank Exported 3- SERP's Changed as well