There is a difference, sometimes, between the PageRank shown in the Google Directory when compared to the PageRank shown in the Google Toolbar. Also, the PageRank values Google has internally are normally different from both the Directory and Toolbar PageRank values.
Gabs showed an example of a change. If you look at the cached version of this page, it shows a PageRank value of 3 for Abbey Theatre but the current version shows a PageRank value of 2 (I may be off on those numbers, but you can clearly see the current version of the PageRank bar is less than the cached or older version. Here is a side by said:
Forum discussion at Search Engine Roundtable Forums.