Slides from my Percona Live talk evaluating the new spatial features in MySQL 5.6 and MariaDB 5.5 are now online. This is new material I have never presented before. It is based on work I have done in my job at Nokia HERE.com location services. So even if at this conference it draws less attention than my HA talks, it is actually what I'm most proud of to present.
TL;DR summary is that PostgreSQL has lots of features but MySQL has much better ease of use and performance. (I copy paste this standard sentence into any PostgreSQL vs MySQL evaluation I do :-) The MongoDB info is basically outdated, as the new 2.4 release introduces completely new implementation based on GeoJSON, new indexing, neither of which I tested.