I commented on some indexing issues I have seen, it may have some relevance on this forum (
http://www.v7n.com/forums/google-for...rp-theory.html)
Maybe PR is 'active' all the time as well, seo-omg-1 mentioned this, makes sense as google have thousands(millions) of items to track the idea of 'storing' the PR index up for months make no sense from a data storage level, it means every day you store that PR index so in 3 months you can release it.
Way to much space involved and computing power and backups etc.
PR must be live, toolbat PR is just the average across the PR index servers anyway, these servers will be updated by their own set of rules/spiders etc so there will be fluctuations while all this information gets propgated around them all.
Across a cross-section of sites, the PR on my toolbar can be different to my friends toolbar in NZ (I am in the UK). His toolbar talks to different PR index servers to mine so its all relevant to where you are anyway.