I have a question. Let's say my site has 10 backlinks from PR0 pages that after the update will be PR10 (impossible but keep reading). When PR update kicks in, will I get PR0 boost from that pages (until next update) or I will get PR10 boost from that pages? That's because I have many backlinks from low PR pages that will have their PR increased after google update.
I think you, like many have been a little misinformed about pagerank. You should take a look here: http://www.mattcutts.com/blog/more-info-on-pagerank/
PR is unimportant. It doesn't effect anything. If a site gains more backlinks after you get alink the link importance will be updated and you will get more importance. What ever PR you get is meaningless.
For me, it's meaningless, but for PRholics, alexaholics and backlinkholics that consider purchasing ads on my site, it's meaningful.
I purchaase links and don't worry about PR. If you provide proof that your PR2 site is getting 10,000 hits a day they won't worry about the PR.