Oh yeah - I remember working with a guy who absolutely insisted that we build application-level sharding into what we were working on (i.e. each primary key would have some metadata that our application logic would use to route traffic to the correct Postgres instance). Our database was not big - 10s of gigabytes - but Instagram did something similar and we needed to be able to scale. I pushed back hard, and fast forward two years and the application was decommissioned without hitting any sort of Postgres bottleneck.