I noticed that too. most of my inner pages changes it pr.... some increased and some decreased ... but no change for the main page pr. even it changes... but it's not affect my website traffic at all ...
not noticed PR changes yet, but yes, the keyword postions keep changing these days, one day I am on 3rd, next day on 9th.
Very true, I have experienced the same thing, and almost always url changes, dns change etc was involved. But sometime there is glitch in google too. This is in no way can be attributed to reciprocal linking etc.
Some of my blogs dropped their pr to 0, some other got pr1-2, but most of them haven't changed. I think it will happen every week or two.