One of the recent changes that occurred recently is the penguin update of Google, the largest online search engine. Not everyone will try to understand or be bothered by this but updates are meant to provide users with the most relevant search results. Google displays search results based on an unknown algorithm that continuously evolve while website owners continue to improve (?) their websites and manipulate content presentation trying to figure out how to be on the top results.
When Google implements update, it's like a bubble bursting for online earners / website owners whose big percentage of their income are coming from Google Adsense. Results that were previously on the first page maybe buried to you-don't-know-what-results-page. This is due to many reasons which may include keyword stuffing as onsite optimization method or spam backlinking to increase website's authority for the targeted keyword. From thousands dollars, online earnings may be lowered to just hundreds and sometimes merely tens after an update because of the decline in the number of visitors. It may take time before the income climb to its previous level, if it can still recover.
Another update is said to be implemented after the penguin. Providing site visitors and clients with useful information will still remain but how the information is presented will surely affect SEO methods and tactics for online marketing.