The ranking changes may be specific to a subset of sites or a larger but still not major ranking algorithm change.
Some say the ranking changes are only in Google UK but others are saying it is specific site penalties.
I'm in the UK and I've seen some of my sites drop too today, I suspect a shake-up. In my experience it sometimes settles back to normal after a day or two, here's hoping!
Honestly, it is way to early to make any assumptions based on forum discussions right now. But I figured I see if anyone else has noticed anything recently?