You can easily check your Keyword Rankings, I usually monitor around 10 keyword which is on first position on SERPs. If any 5 of them are out of 1st page after Penguin Update then you can notice ranking drop...
Some of my Keyword on first page of Google.com are "sem tips" "seo guest post" "twitter marketing trends" "does adwords help seo" "Importance of Affiliate Marketing in 2013" I guess these are top 5 results.... there are other keywords too but my trial SEO software does not allow me to get more..
If you search these keywords without qoutes then you can find my blog ebuzznet