1 They never contacted me with their perceived issue. I only know about it because of the endless retweets.
2 Out of the tens of thousands of users who have upgraded, exactly one (quickonlinetips.com) has reported having a pagerank drop.
3 The fact that their pagerank dropped isn't even close to evidence that All in One SEO Pack is the cause.
4 Even if All in One SEO Pack's new feature is the cause, they should have checked the options page when upgrading. This feature, like many others, is turned on by default. The documentation has always informed users that the recommended configuration is set by default in the plugin. So if that's my fault, I see two courses of action for this:
a) I can stop releasing updates for the plugin (I doubt most people want that)
b) I can have new functionality disabled by default (Since the person complains that I enabled the feature by default upon upgrade, this would resolve the issue for them. However, their whole basis for their complaint is that they didn't check for the new options. So if I go this route, there's no point in me ever releasing updates to begin with.)
5 The new version of the plugin has been out a week. So they've had this version for no longer than that. You can do your own research as to whether or not a site's public PR can drop from whatever they claim to have been to a PR 4 in that amount of time.
For what shall it profit a man, if he shall gain the whole world, and lose his own soul?