As tweeted by Matt Cutts, late night on Friday 25th May, Google pushed minor data refresh effecting <0.1% of English searches
Matt Cutt said on twitter
Minor weather report: We pushed 1st Penguin algo data refresh an hour ago. Affects <0.1% of English searches. Context:https://goo.gl/4f7Pq
No major changes has been noted from webmasters on forums and webmaster communities, so it may be those small % of sites which was penalized wrongly by Google as reported on various SEO forums or which may be big brands.
As we know that Google’s Penguin algorithm effected many sites due to low quality links.
We can expect more such refreshes in coming days so that Google can lift the filter from those sites which already removed bad links as reported by Google.