Unless you're selling links (maybe not a Google-favored practice right now), don't obsess over PageRank. Rather, go about to secure the good backlinks that will bring good PR to your web pages, and just let the PR itself fall where it will.
Till now I have not seen any pagerank movement, I do not think Google update that regularly. A interval of a few months maybe
Don't forget the link traders. It's the guys that are about to link to you that are obsessing over PageRank.
I'd much rather have a website with PR0 and 100,000 pageviews/month, than a PR5 with 1,000 pageviews/month.
PR updates typically run every 3 to 4 months. The next one is due anytime now through the middle of January. But seriously - and as I've said before - don't worry so much about PR. Instead, focus on good content and linking practices, and PR will take care of itself.
I don't think that we will see an export around Christams. january is the normal month for the udate to the toolbar.