There are some very early reports in the WebmasterWorld thread and some comments here that are suggesting Google might be pushing out a Penguin update now.

It is way too early to be confident there is an update happening right now, but there are some early warning signs.

Pete Hall at WebmasterWorld said:

What on earth has gone down in the UK today?

I’ve seen a site drop a huge amount.

Penguin?

Richard Merry commented here saying:

Again, these are just early warning signs.

It might be something completely unrelated to Penguin or Panda but it is hard to tell right now.

The last Penguin refresh was on May 25th and the last Panda refresh was on June 24th, so we are definitely due a Penguin refresh.

Forum discussion at WebmasterWorld.