This is indeed a recurring theme, which has happened several times in the past (Florida update, sandboxing introduction, Jan
PR update shuffle)and seems to be consistent with Google's ongoing battle to stay one step ahead of the SEOs.
Of course, it usually starts out as an experiment to avoid spammers, then google realises that decent sites are getting penalised - no doubt they have their experts reading threads on respectable forums like this and take their cue, eventually they revert to their sensibilities and everything settles down. In the meantime however, some webmasters panic and make all sorts of changes which adversely effect them in the long term.
I think we all (google algo technicians included) need to recognise that
SEO isn't going to go away - and as long as you are the best SE out there, everyone is going to try and beat their way to the top by whatever means necessary. The algo just gets more sophisiticated but as long as everyone's intentions are essentially ethical, then common sense will prevail.
My advice from personal experiences is: do nothing, wait and see, things setttle down after a few weeks.
SEO'd sites provide the best content usually because they are striving to generate income and this helps them maintain good content. Google wouldn't risk tarnishing their reputation for results by penalising good content because it was
SEO'd.