We use a lot of PostGIS via GeoDjango, and I made a mental note to remember this article if I my postgres instances ever start ailing. Unfortunately, we haven't pushed these limits nearly as much as Instagram.
Just a +1 on this. PostGIS and PostgreSQL are completely awesome. I've been doing a lot of geospatial projects recently and have been stunned by just how fast, robust and scalable PostGIS and PostgreSQL are. If you're storing latitudes/longitudes in a database then check out PostGIS now.