on Just Publishing Advice:
For many bloggers, a Google Update can come as a nasty shock.
You might have been sailing along for years with steady increases in your organic traffic and then, crash.
The chances are that because you were unaffected by previous changes, you didn’t pay much attention to Google algorithm updates.
But it certainly gets your attention when you suddenly lose 30, 40 or 50% of your organic traffic overnight.
Legends of Windemere 