In a very short answer, Caffeine is Google's answer to the overwhelming pace of content creation on-line. Before Caffeine was launched the results that you were not getting the newest results but rather the strongest ones (in terms of SEO). According to Google, the new features made the results 50% "fresher". I will not write Caffeine's effects on SEO and what can you do in order to fit your site to this new reality because its quite long, but I will be more than happy to help you if you want. Just PM if you are interested. Good Luck!