This comes courtesy of Bridget Jung, Chief Creative Officer - Digitas
I'd also recommend this nice roundup from AdWeek of all the Grand Prix winners for 2012.
Adverblog has a nice article on the overall Macro trends among the winners that's quite nice.
Last but not least, Contagious Magazine has a nice breakdown which includes snippets/quotes from about the work in each category.
But again, it's really worth spending some time on the Cannes Lion site and checking out the various winners across categories and the corresponding case study videos.