I would like to know if Guest posting is really recommended post Penguin updates and if it is very beneficial in SEO.
yeah it is always recommended if you are able to post in relevant and authoritative site. But your content must be high quality. you can get a lot of point here http://www.seomoz.org/q/is-guest-posting-still-a-good-idea
Still, Guest Posting have a value in SEO because Google always wanted unique content and quality backlinks. If you provide both things then Google increase your ranking in SERP
Yes in panda update some of the focus has shifted to Guest posting and getting links through it.this has become one of the best ways to get context based links that bring link juice and traffic and increase the readers or followers and ultimately revenue.