Following Uber's case discussion, I found this talk by Alexey Kopytov to be really interesting: http://kaamos.me/talks/pgday16/strongmysql/strongmysql.html (online html, in Russian)
I translated it to English: https://www.dropbox.com/s/t6a15s66jxg50tg/mysqlstrong_pgday16russia.pdf?dl=0 (pdf) The slides deck contains a lot of details. The author claims that during recent years, MySQL made a lot of progress in defending and advancing its position as a "most popular database for the web", he provides detailed reasoning for that, and then concludes that PostgreSQL will need years and maybe even decades to close gaps in the certain fields which are very sensitive for large companies: - replication - storage engines / compression / direct IO / etc - partitioning, etc. Of course this information is biased (Alexey works at Percona) but IMO it's much more detailed, qualitative and useful analysis compared to the Uber's recent article.
