The Google Penguin and Panda updates focused largely on quality of content. Google's search algorithm initially encouraged the creation of content with links from that content to another place. If you had a website and wanted it to rank well then one viable strategy was to create content and link from it to your website. Because it takes longer to write good, well researched content than simply put words on paper Google unfortunately encouraged people to fill the internet with spam.
To redress this Google introduced Penguin, Panda and, more recently, Hummingbird. It is now said that updates are an ongoing state. So, there are days when things change more than usual but the algorithm is in a constant state of flux.
The main updates addressed such problems as:-
Thin content: Pages created for SEO with very little content.
Keyword spamming: Pages full of keywords with little of value for the reader.
Spinning: Taking one article and changing words to make several articles.
Link spam: Keyword rich hyperlinks designed to game the Google algorithm.
There are various other practices which Google has clamped down on. Many websites have lost their power because they have fallen foul of these quality moves.
It is important to understand TrustRank. The most trusted websites have very few links to poor quality content. The websites they link to again have relatively few bad links. At the second link hop you find more spam and then it takes a significant leap at the next hop. It shows you how quickly and how easily a website moves away from trust.
Essentially Google aims to remain the search engine of choice. It will reward content that is created to satisfy the user who has searched for it. If your website encourages quality and polices poor quality then your aims are congruent with Google's and you will not find your website penalised.
Matt Cutts, Google's main conduit between them and the SEO industry, has said that before you publish content you should ask yourself whether you would expect to see it in a quality magazine. That is probably the best way to look at whether your site should host content.