I recently made the discreet purchase of text links for one my sites. On October 23, when Google updated PR, the site went from PR0 to PR2. Here's my question: Does Google ever update an individual site's PR between regular updates?
Yes surely google updates each time. If you need more links check this site by me "jeetlo.com" I hope it can be useful for you to improve PR as I got PR 4 in just three months with an incredible improvement in my alexa rank also.
Google updates ranking measures (including PR) all the time, but it does not update the toolbar PR but every so often. So a good strong link can get you lots of SERPs well before your PR shows any changes in the toolbar.